Clinical Course and Extended Survival in a Canine Patient with Pericardial Mesothelioma Managed Without Chemotherapeutic Intervention

Clinical Course and Extended Survival in a Canine Patient with Pericardial Mesothelioma Managed Without Chemotherapeutic Intervention | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report Clinical Course and Extended Survival in a Canine Patient with Pericardial Mesothelioma Managed Without Chemotherapeutic Intervention Seol-Gi Park, Joungsun Moon, I-se O, Daesik Kim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6302384/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Pericardial mesothelioma is an uncommon and aggressive neoplasm in dogs, typically associated with poor prognosis and limited therapeutic options. Although chemotherapy is frequently used, there is a scarcity of literature describing effective management strategies without chemotherapeutic intervention. This case is reported due to its rarity and the exceptionally long-term survival achieved through non-chemotherapeutic, multimodal management. Case presentation A 7-year-old spayed female Pomeranian presented with acute respiratory distress caused by pericardial effusion. The initial management involved pericardiocentesis and medical therapy, but recurrence of effusion necessitated surgical intervention. Subtotal pericardiectomy was performed, and malignant pericardial mesothelioma was confirmed histopathologically. A thoracic port was implanted postoperatively for ongoing effusion management. Remarkably, the patient remained clinically stable and maintained a good quality of life for 21 months (628 days) without chemotherapy, supported by regular monitoring and comprehensive symptomatic care. Conclusions This case underscores the clinical importance of individualized, multimodal therapeutic approaches in the management of canine pericardial mesothelioma. It highlights that prolonged survival can be achieved through aggressive effusion control and surgical interventions, even in the absence of systemic chemotherapy. The findings provide valuable insights and potential implications for veterinary clinicians handling similar challenging neoplastic cases. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Background Pericardial and pleural effusions constitute significant pathophysiological sequelae in canine patients with cardiovascular and pulmonary disorders, potentially precipitating life-threatening clinical manifestations if inadequately managed. Among the diverse etiologies, malignant mesothelioma represents an uncommon yet clinically significant neoplasm affecting the mesothelial lining of serosal surfaces, including the pericardium, pleura, and peritoneum. In canine patients, pericardial mesothelioma is recognized as a significant neoplastic cause of pericardial effusion, alongside hemangiosarcoma and chemodectoma[ 1 , 2 ]. The disease typically demonstrates an insidious progression, with clinical manifestations becoming apparent only after substantial effusion accumulation results in cardiac tamponade or respiratory compromise[ 3 ]. The etiopathogenesis of mesothelioma in canines remains poorly understood. While asbestos exposure represents a well-established risk factor for mesothelioma in human patients, a definitive causal relationship has not been established in veterinary medicine [ 4 , 5 ]. Histopathologically, mesothelioma is classified into epithelioid, sarcomatoid, and biphasic subtypes, with the epithelioid form predominating in clinical presentations Diagnostic evaluation is challenging, as conventional imaging modalities such as thoracic X-rays, echocardiography, and computed tomography (CT) often miss discrete mass lesions[ 6 , 7 ]. However, cytological analysis of pericardial fluid often reveals reactive mesothelial cells, necessitating histopathological examination for a definitive diagnosis[ 7 ]. CT imaging may demonstrate pleural nodularity, pericardial thickening, or intrathoracic lymphadenopathy, potentially supporting a diagnosis of mesothelioma[ 1 , 7 , 8 ]. However, fine-needle aspiration cytology and histopathology remain critical for confirmation[ 7 , 9 ]. Therapeutic management of pericardial mesothelioma is predominantly palliative, aiming to alleviate symptoms and improve quality of life. Subtotal pericardiectomy is commonly performed to prevent recurrent cardiac tamponade, providing short-term clinical benefit [ 6 ]. Systemic chemotherapy protocols, including carboplatin or doxorubicin-based regimens, have been investigated in selected cases, though their therapeutic efficacy remains uncertain. Intracavitary chemotherapy has shown promise in delaying effusion recurrence but has not demonstrated a clear survival advantage [ 10 ]. Reported median survival intervals demonstrate significant variability, ranging from 74 to 366 days, depending upon the therapeutic approaches implemented[ 2 ]. Although the prognosis for pericardial mesothelioma is generally poor, the present case report describes a canine patient who survived for more than 12 months through proactive effusion management, pericardiectomy, and comprehensive supportive care. This case underscores the clinical significance of consistent monitoring protocols and multimodal therapeutic approaches. By presenting a detailed analysis of the clinical presentation, therapeutic interventions, and outcome measures, this report aims to provide valuable guidance for veterinary practitioners managing similar cases, emphasizing the significance of early intervention and multimodal treatment strategies in optimizing patient outcomes. Case presentation A 7-year-old spayed female Pomeranian, weighing 4.58 kg, presented with acute-onset respiratory distress, unproductive cough, and occasional gagging, persisting for approximately 24 hours (Day 0). The patient maintained a normal appetite, though the owner noted concurrent lethargy. Physical examination revealed tachypnea with shallow respiratory patterns and muffled heart sounds on thoracic auscultation. Thoracic radiographs revealed marked cardiomegaly with a vertebral heart score (VHS) of 14.3 and radiographic features suggestive of pleural fluid accumulation (Fig. 1A). Subsequent echocardiography confirmed a moderate pericardial effusion and mild tricuspid valve regurgitation, with no evidence of discrete intracardiac masses (Fig. 1B). Initial clinical pathology on Day 0 identified respiratory acidosis with decreased pH (7.19), elevated PCO₂ (63.9 mmHg), and reduced buffer base (-5.6 mmol/L), while electrolytes remained within reference intervals. Hematologic analysis showed a hematocrit of 51% and a hemoglobin concentration of 15.8 g/dL. Therapeutic intervention comprised ultrasound-guided pericardiocentesis and thoracocentesis, which removed 50 mL of pericardial fluid and 200 mL(Fig. 5) of pleural fluid, respectively, and led to rapid clinical improvement and resolution of respiratory distress. The patient was subsequently treated with pimobendan (0.3 mg/kg orally every 12 hours), furosemide (1 mg/kg orally every 12 hours), pentoxifylline (20 mg/kg orally every 12 hours), and metronidazole (10 mg/kg orally every 12 hours) to prevent effusion recurrence and mitigate secondary pathophysiological processes. A follow-up echocardiographic assessment on Day 3 identified mild mitral regurgitation (mitral regurgitation pressure gradient 143.8 mmHg) and mild ventricular enlargement (left ventricular internal dimension in diastole normalized 1.45, left ventricular internal dimension in systole 14.71 mm). These findings were consistent with stage B1 myxomatous mitral valve degeneration and stage 2 left ventricular diastolic dysfunction. The examination did not identify discrete intracardiac masses, and minimal residual pleural fluid was noted. The attending clinician diagnosed idiopathic pericardial effusion, although infiltrative cardiac neoplasia remained a differential diagnosis that could not be definitively excluded. The patient maintained clinical stability for approximately nine months before presenting with recurrent respiratory difficulties on Day 275. A thoracic X-ray demonstrated persistent cardiomegaly (VHS 12.2), though respiratory parameters improved during hospitalization. On Day 276, echocardiographic evaluation confirmed recurrent pericardial fluid accumulation necessitating therapeutic drainage of 90 mL. Clinicopathologic evaluation showed mild respiratory acidosis (pH 7.33, PCO₂ 45.8 mmHg), elevated acute phase protein response (C-reactive protein 45 mg/L), and moderate thrombocytopenia (platelet count 148 × 10⁹/L). Cytomorphologic assessment of the pericardial fluid revealed hemorrhagic effusion with mesothelial cell populations and elevated protein concentration (4.0 g/dL), but no definitive neoplastic cellular criteria. Serum biochemical analysis showed that hepatic and renal parameters were within reference intervals. Between Days 276 and 520, the patient required progressively more frequent pericardiocentesis interventions, yielding drainage volumes ranging from 67 mL to 240 mL (Fig. 5). The intervals between procedures were shortened from monthly to biweekly. Adjunctive pharmacologic management comprised tranexamic acid (10 mg/kg orally every 12 hours), metronidazole (10 mg/kg orally every 12 hours), pentoxifylline (20 mg/kg orally every 12 hours), and famotidine (0.5 mg/kg orally every 12 hours), although effusion recurrence persisted. CT scan was performed to investigate what was causing the persistent pericardial effusion and to inform potential surgical options. The CT showed pericardial wall thickening, regional lymphadenopathy, and nodular lesions within the mediastinum (Fig. 2). Following the CT scan, pericardiectomy was performed for diagnostic and therapeutic purposes, and a thoracic port was placed to manage pleural effusion (Fig. 4). Cytological analysis of the pericardial fluid (Fig. 3A) identified clusters of mesothelial cells exhibiting moderate nuclear anisokaryosis, finely granular chromatin, and abundant eosinophilic cytoplasm. Scattered erythrophagocytic macrophages and mild neutrophilic infiltration were also observed. Although atypical mesothelial cells raised suspicion for a neoplastic process, definitive cytological criteria for malignancy and invasive behavior were not conclusively observed, underscoring the need for histopathological confirmation. Histopathological examination of the pericardial tissues (Fig. 3C, 3D) revealed neoplastic mesothelial cells forming papillary and glandular structures supported by fibrovascular stroma. The tumor cells displayed prominent nucleoli, moderate nuclear pleomorphism, and abundant eosinophilic cytoplasm. Occasional mitotic figures were observed, and infiltration into underlying connective tissue was also seen (Fig. 3D, arrows). These findings confirmed a diagnosis of malignant pericardial mesothelioma. Despite undergoing subtotal pericardiectomy and concurrent placement of a thoracic drainage port, the pleural effusion recurred progressively from Day 540, necessitating regular drainage via the previously implanted thoracic port. Drainage volumes per session ranged from 70 to 240 mL, with intervals initially between seven and 10 days, which progressively shortened over time(Fig. 5). Cytological analysis of the drained pleural fluid revealed moderate cellularity (white blood cell (WBC) count of 10.21 × 10³/μL) and elevated protein concentration (4.0 g/dL), primarily comprising atypical mesothelial cells with moderate nuclear pleomorphism, fine chromatin, and abundant eosinophilic cytoplasm (Fig. 3B). Although these cytological findings alone were insufficient to definitively differentiate malignant mesothelioma from reactive mesothelial proliferation, subsequent histopathological evaluation of the pericardium confirmed malignant features, including the invasion of neoplastic mesothelial cells into adjacent connective tissue. These findings corroborated the diagnosis of malignant pericardial mesothelioma. Because of ongoing clinical deterioration, oral prednisolone was initiated on Day 620 at a dose of 0.5 mg/kg daily, which was subsequently increased to 1 mg/kg twice daily. The initial response to prednisolone therapy was favorable, temporarily extending intervals between fluid drainage procedures. However, by Day 626, thoracic drainage was required every 1–2 days, with fluid removal volumes ranging from 80 to 120 mL(Fig. 5). The patient’s body weight fluctuated between 5.88 kg and 6.02 kg during this period. Despite intensive supportive care and repeated thoracic fluid drainage, the patient’s clinical condition progressively worsened. On Day 627, scheduled thoracic fluid drainage was deferred due to the patient's severely compromised condition, and the patient subsequently succumbed to respiratory arrest on Day 628. The overall survival was approximately 21 months (628 days) following the initial presentation of pericardial effusion. CT images revealing pericardial thickening, regional lymphadenopathy, and nodular changes in the mediastinum, consistent with malignant pericardial mesothelioma. Discussion and Conclusions This case report describes a rare instance of prolonged survival (21 months) in a dog diagnosed with malignant pericardial mesothelioma, managed without chemotherapy. This outcome emphasizes the critical role of systematic pericardial and pleural fluid management, subtotal pericardiectomy, and supportive therapies in optimizing survival and maintaining quality of life. Previous studies have documented median survival times (MST) for canine malignant pericardial mesothelioma ranging from 74 to 366 days, depending on the treatment approach[1, 2]. While surgical intervention and adjunctive therapies have been associated with extended survival, overall prognosis remains guarded, with only 22% of affected dogs surviving beyond one year 1,8]. The 21-month survival observed in this case underscores the potential benefits of proactive medical and surgical management in prolonging survival and improving quality of life. Establishing a definitive diagnosis was initially challenging because of the non-specific clinical presentation and inconclusive cytological findings. Thoracic radiographs, echocardiography, and CT identified pericardial thickening and pleural effusion but missed the discrete intracardiac masses, complicating the diagnostic process. These findings align with previous reports describing the diagnostic challenges posed by the infiltrative and diffuse nature of canine mesothelioma[1, 11]. Cytological evaluation of pericardial and pleural fluid (Fig. 3A, 3B) revealed atypical mesothelial cells with anisokaryosis and occasional nucleoli, but definitive malignant characteristics were absent. Given the inherent limitations of cytology in differentiating reactive mesothelial proliferation from neoplastic transformation, histopathological examination was necessary for a conclusive diagnosis. Histopathological analysis of the excised pericardium confirmed malignant pericardial mesothelioma, characterized by papillary and glandular proliferations of mesothelial cells displaying moderate nuclear pleomorphism, abundant eosinophilic cytoplasm, prominent nucleoli, and occasional mitotic figures, with invasion into adjacent connective tissues (Fig. 3C, 3D), consistent with previously described histologic features of canine pericardial mesothelioma[1, 12, 13]. Although cytological analysis of pericardial and pleural fluid identified atypical mesothelial cells, the findings lacked definitive features of malignancy. This underscores the limited sensitivity and specificity of cytology in detecting pericardial mesothelioma and highlights the importance of histopathological evaluation for definitive diagnosis[1, 2, 12, 14]. In this case, systemic chemotherapy was not undertaken; instead, therapeutic interventions included subtotal pericardiectomy and concurrent thoracic port placement. Subtotal pericardiectomy alleviated recurrent cardiac tamponade, a common complication of pericardial mesothelioma, thereby improving cardiac function and clinical status [5]. Additionally, the thoracic port facilitated the long-term management of recurrent pleural effusion, contributing significantly to the patient’s clinical stability and quality of life. Several prognostic factors potentially contributed to the extended survival time observed in this case. Early recognition of clinical signs and immediate therapeutic interventions likely prevented severe cardiac dysfunction and secondary organ impairment. Additionally, a structured follow-up protocol involving consistent clinical evaluations and fluid management facilitated timely interventions that helped maintain clinical stability. Another essential factor was the high level of owner compliance with the therapeutic regimen, enabling effective long-term management. Finally, the patient's relatively young age at diagnosis (7 years) and lack of significant concurrent conditions likely improved tolerance to repeated invasive procedures and physiological resilience, further supporting prolonged survival. The progression from primary pericardial involvement to subsequent pleural effusion reflects a characteristic pattern of malignant mesothelioma dissemination. Typically, mesothelioma originates as a diffuse neoplastic transformation of mesothelial cells lining the pericardium, spreading insidiously into adjacent structures rather than forming clearly defined masses[11, 15, 16]. This infiltrative growth pattern accounts for the initial diagnostic challenges and the absence of discrete masses on imaging. A pleural effusion developing after pericardiectomy likely represents a direct extension of the neoplastic process to the pleural cavity, consistent with the locally aggressive nature of mesothelioma[17]. The post-pericardiectomy shift from predominantly pericardial to pleural effusion may be explained by the removal of the pericardial barrier, which reduced resistance and allowed fluid to accumulate preferentially in the pleural space[17, 18]. This pattern of disease progression highlights the importance of viewing pericardial and pleural spaces as interconnected in mesothelioma cases, with implications for both diagnostic approaches and therapeutic interventions[19]. Throughout the patient's clinical course, a gradual increase in body weight was observed, from 4.58 kg to 6.02 kg over the follow-up period. Such sustained weight gain, despite the underlying malignancy and repeated therapeutic interventions, is a positive prognostic factor, indicating effective symptom control and adequate nutritional support[20, 21]. Previous studies have suggested that maintaining or improving body weight and body condition score (BCS) in dogs with chronic or neoplastic conditions correlates positively with prolonged survival and enhanced quality of life[20, 21]. Conversely, weight loss represents a negative prognostic factor, particularly in patients with chronic disorders including cardiac disease and neoplastic conditions[20, 22]. Moreover, long-term surveillance studies of animals with pericardial fluid accumulation suggest that maintaining body condition correlates with longer overall survival[17]. The association between stable body weight and survival appears multifaceted. For example, stable body weight is indicative of effective control of disease-associated clinical signs including nausea, discomfort, and respiratory compromise[23]. Additionally, stable body weight suggests the preservation of muscle tissue, supporting systemic physiological processes and potentially enhancing resilience to repeated interventions. The absence of cancer-associated cachexia in this patient, despite histologically confirmed malignancy, may reflect the localization of the neoplastic process due to aggressive management[24]. In light of these findings, we recommend methodical nutritional evaluation, consistent body weight monitoring, and client education regarding dietary management as essential elements of comprehensive long-term care protocols for comparable cases. These nutritional considerations may significantly influence therapeutic outcomes in patients with chronic life-limiting disorders. This single-case report has several limitations, including its retrospective design and the inherent constraints of individual case documentation. Additionally, as chemotherapeutic intervention was not implemented, definitive comparisons between chemotherapy and supportive management cannot be established. Notwithstanding these limitations, our observations can provide valuable clinical perspectives for managing similar cases, particularly emphasizing that comprehensive effusion control and appropriate surgical management alone can significantly extend overall survival. Clinical recommendations derived from this case include a sequential diagnostic protocol beginning with non-invasive or minimally invasive techniques, such as thoracic imaging, cardiac ultrasonography, and fluid analysis. When initial diagnostic results are inconclusive, other imaging modalities (e.g., CT) and tissue sampling should be pursued for accurate diagnosis and treatment planning. Monitoring frequency should be adjusted according to effusion recurrence patterns. For this patient, evaluations every two weeks were initially adequate, with subsequent transition to more frequent assessments (weekly, or more often) as their condition progressed. Bespoke monitoring protocols can optimize the balance between effective clinical surveillance and client adherence. Prompt consideration of subtotal pericardiectomy is indicated for cases with recurrent effusion unresponsive to medical therapy, as this intervention both reduces cardiac tamponade risk and provides diagnostic tissue specimens. In patients experiencing rapid pleural fluid reaccumulation, placing an indwelling thoracic port should be considered, as it facilitates efficient fluid removal while reducing patient anxiety and the need for sedation or anesthesia. Further investigation is necessary to evaluate the comparative effectiveness of various therapeutic strategies, including chemotherapy, surgical interventions, and palliative care, in canine pericardial mesothelioma. Multi-institutional studies examining survival outcomes across different treatment approaches would provide valuable data to enhance prognostic accuracy and develop evidence-based clinical guidelines. This case described a dog with pericardial mesothelioma that survived for 21 months without chemotherapy. The treatment plan involved sequential effusion drainage, subtotal pericardiectomy, and thoracic port implantation. Our findings suggest that survival can be prolonged without chemotherapy, which may be important in clinical scenarios when the owners refuse chemotherapy or it is considered unsuitable. Further validation of these observations through larger case series would allow refinement of protocols. Abbreviations BCS: Body Condition Score CHF: Congestive Heart Failure CT: Computed Tomography VHS: Vertebral Heart Score WBC: White Blood Cell PCO₂: Partial Pressure of Carbon Dioxide MST: Median Survival Time Declarations Acknowledgements The authors extend their sincere gratitude to the veterinary staff for their dedicated care and technical support during the dog's treatment and hospitalization. Author contributions DK and SGP summarized the data and drafted the manuscript. DK, SGP, JSM, and ISO managed clinical treatment and provided patient care. All authors read and approved the final manuscript. Funding This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Data availability All datasets are available in the main manuscript Ethics approval and consent to participate The patient was treated at the owner's request, with informed consent for the treatment process. Clinical data were collected throughout the course of treatment, and written consent was obtained from the owner for the use of medical data for educational and research purposes. Consent for publication Written consent for publication was obtained from the dog’s owner. All identifying information was excluded, and all images used in the manuscript were obtained during the diagnostic and treatment process with the owner's permission. Competing interests The authors declare that they have no competing interests. References Moberg HL, Gramer I, Schofield I, Blackwood L, Killick D, Priestnall SL, et al. Clinical presentation, treatment and outcome of canine malignant mesothelioma: A retrospective study of 34 cases. Vet Comp Oncol. 2022;20:304–12. Lajoinie M, Chavalle T, Floch F, Sayag D, Lanore D, Ponce F, et al. Outcome of dogs treated with chemotherapy for mesothelioma: A retrospective clinical study on 40 cases and a literature review. Vet Comp Oncol. 2022;20:825–35. Stepien RL, Whitley NT, Dubielzig RR. Idiopathic or mesothelioma-related pericardial effusion: Clinical findings and survival in 17 dogs studied retrospectively. J Small Anim Pract. 2000;41:342–7. Glickman LT, Domanski LM, Maguire TG, Dubielzig RR, Churg A. Mesothelioma in pet dogs associated with exposure of their owners to asbestos. Environ Res. 1983;32:305–13. Machida N, Tanaka R, Takemura N, Fujii Y, Ueno A, Mitsumori K. Development of pericardial mesothelioma in golden retrievers with a long-term history of idiopathic haemorrhagic pericardial effusion. J Comp Pathol. 2004;131:166–75. Scheuermann LM, Gordon-Evans WJ, Nault AJ. Systematic review of the treatment options for pericardial effusions in dogs. Vet Surg. 2021;50:20–8. Rivera PA, Borgarelli M. Cardiovascular images: constrictive pericarditis and tricavitary effusion in a dog with pericardial mesothelioma. J Vet Cardiol. 2020;32:55–9. Thrall DE, Goldschmidt MH. Mesothelioma in the Dog: Six Case Reports. Vet Radiol. 1978;19:107–15. Min JH, Yoon J, Son S, Song WJ, Lee S, Yun Y, et al. A Rare Case of Canine Pericardial Malignant Mesothelioma: Clinicopathologic Findings, Diagnostic Investigations, and Clinical Course with Epirubicin Treatment. J Vet Clin. 2024;41:170–7. Nabeta R, Kanaya A, Elbadawy M, Usui T, Furuya T, Suzuki K et al. Chemosensitivity of three patient-derived primary cultures of canine pericardial mesothelioma by single-agent and combination treatment. Front Vet Sci. 2023;10. Rivera PA, Borgarelli M. Cardiovascular images: constrictive pericarditis and tricavitary effusion in a dog with pericardial mesothelioma. J Vet Cardiol. 2020;32:55–9. Nabeta R, Kanaya A, Elbadawy M, Usui T, Furuya T, Suzuki K et al. Chemosensitivity of three patient-derived primary cultures of canine pericardial mesothelioma by single-agent and combination treatment. Front Vet Sci. 2023;10. Turk JR, Ikede B 0, Zubaidy A, Gill CW. References Request reprints from Pericardial Mesothelioma with Cardiac Tamponade in a Dog. Marcel Dekker; 1976. Morini M, Bettini G, Morandi F, Burdisso R, Marcato PS. Deciduoid Peritoneal Mesothelioma in a Dog. Closa JM, Font A, Mascort J. Pericardial mesothelioma in a dog: Long-term survival after pericardiectomy in combination with chemotherapy. J Small Anim Pract. 1999;40:383–6. Brower A, Herold LV, Kirby BM. Canine Cardiac Mesothelioma with Granular Cell Morphology. 2006. Stafford Johnson M, Martin M, Binns S, Day MJ. A retrospective study of clinical findings, treatment and outcome in 143 dogs with pericardial effusion. J Small Anim Pract. 2004;45:546–52. Dunning D, Monnet E, Orton EC, Salman MD. Analysis of prognostic indicators for dogs with pericardial effusion: 46 cases (1985–1996). J Am Vet Med Assoc. 1998;212:1276–80. Withrow SJ, Vail DM, Page R. Withrow and MacEwen’s Small Animal Clinical Oncology. Elsevier Health Sciences; 2012. Michel KE, Sorenmo K, Shofer FS. Evaluation of body condition and weight loss in dogs presented to a veterinary oncology service. J Vet Intern Med. 2004;18:692–5. Saker KE, Remillard RL. Critical care nutrition and enteral-assisted feeding. Small Anim Clin Nutr. 2010;5:441–2. Hubbard WN, Fish DR, McBrien DJ. The use of impedance cardiography in heart failure. Int J Cardiol. 1986;12:71–9. Anthony RM, Amundson MD, Brejda J, Becvarova I. Acceptance of a Novel, Highly Palatable, Calorically Dense, and Nutritionally Complete Diet in Dogs with Benign and Malignant Tumors. Vet Sci. 2023;10. Freeman LM. Cachexia and sarcopenia: Emerging syndromes of importance in dogs and cats. J Vet Intern Med. 2012;26:3–17. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6302384","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":456681531,"identity":"62790b22-5a51-47de-aa53-09244000dcea","order_by":0,"name":"Seol-Gi Park","email":"","orcid":"","institution":"Incheon Sky Animal Hospital","correspondingAuthor":false,"prefix":"","firstName":"Seol-Gi","middleName":"","lastName":"Park","suffix":""},{"id":456681532,"identity":"a38e049b-0565-45fc-af5e-682df70a2f3a","order_by":1,"name":"Joungsun Moon","email":"","orcid":"","institution":"Incheon Sky Animal 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effusion\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6302384/v1/93b4d801d6e0f1835d62b1d2.jpg"},{"id":83108188,"identity":"2baa98fc-3eda-48f5-a810-309c07ca1b7e","added_by":"auto","created_at":"2025-05-20 06:46:43","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":22556,"visible":true,"origin":"","legend":"\u003cp\u003eComputed tomography (CT) findings at diagnosis\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6302384/v1/9a1a3ef72ccdcc121ea18926.jpg"},{"id":83108193,"identity":"18de5960-fd42-4855-bfce-d08f840ecb9c","added_by":"auto","created_at":"2025-05-20 06:46:43","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":278628,"visible":true,"origin":"","legend":"\u003cp\u003eHistopathological and cytological findings.\u003c/p\u003e\n\u003cp\u003e(A) Cytological analysis of pericardial fluid(x400) showing clusters of mesothelial cells with moderate anisokaryosis, fine chromatin, and eosinophilic cytoplasm.\u003c/p\u003e\n\u003cp\u003e(B) Cytology of pleural effusion(x400) demonstrating mesothelial cells with nuclear pleomorphism and occasional nucleoli.\u003c/p\u003e\n\u003cp\u003e(C) Histopathology of the pericardium(x100) showing papillary and glandular proliferations of cuboidal mesothelial cells supported by fibrovascular stroma.\u003c/p\u003e\n\u003cp\u003e(D) High-power view of pericardial tissue(x400) showing neoplastic mesothelial cells with prominent nucleoli, moderate nuclear pleomorphism, and infiltration into the underlying connective tissue (arrows), confirming malignant pericardial mesothelioma.\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6302384/v1/5ec724204aab9e475368ee86.jpg"},{"id":83109601,"identity":"ca3a87b0-84ea-4508-93cb-35a82938dced","added_by":"auto","created_at":"2025-05-20 07:02:43","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":355834,"visible":true,"origin":"","legend":"\u003cp\u003eLong-term management following pleural port placement.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6302384/v1/f5f7f340c7203b7eeb370968.jpg"},{"id":83108195,"identity":"cfd60122-6172-4d29-8e7a-f58d690402ba","added_by":"auto","created_at":"2025-05-20 06:46:43","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":127200,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in pericardial and thoracic fluid drainage and body weight over time in a dog with malignant pericardial mesothelioma.\u003cbr\u003e\nPericardial and thoracic fluid drainage volumes (mL) and body weight (kg) were monitored throughout the disease course. \"Day\" indicates time since diagnosis. Fluid drainage (mL) reflects pericardial and thoracic centesis volumes.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6302384/v1/c24bb0936bff29f82d6adb5d.jpg"},{"id":90287585,"identity":"7d8fe865-e2ba-487d-8621-a3b81aa991e7","added_by":"auto","created_at":"2025-09-01 06:39:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1295470,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6302384/v1/8a0871a8-a68b-4de7-85c5-f37324c211e2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Clinical Course and Extended Survival in a Canine Patient with Pericardial Mesothelioma Managed Without Chemotherapeutic Intervention","fulltext":[{"header":"Background","content":"\u003cp\u003ePericardial and pleural effusions constitute significant pathophysiological sequelae in canine patients with cardiovascular and pulmonary disorders, potentially precipitating life-threatening clinical manifestations if inadequately managed. Among the diverse etiologies, malignant mesothelioma represents an uncommon yet clinically significant neoplasm affecting the mesothelial lining of serosal surfaces, including the pericardium, pleura, and peritoneum. In canine patients, pericardial mesothelioma is recognized as a significant neoplastic cause of pericardial effusion, alongside hemangiosarcoma and chemodectoma[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The disease typically demonstrates an insidious progression, with clinical manifestations becoming apparent only after substantial effusion accumulation results in cardiac tamponade or respiratory compromise[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe etiopathogenesis of mesothelioma in canines remains poorly understood. While asbestos exposure represents a well-established risk factor for mesothelioma in human patients, a definitive causal relationship has not been established in veterinary medicine [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Histopathologically, mesothelioma is classified into epithelioid, sarcomatoid, and biphasic subtypes, with the epithelioid form predominating in clinical presentations Diagnostic evaluation is challenging, as conventional imaging modalities such as thoracic X-rays, echocardiography, and computed tomography (CT) often miss discrete mass lesions[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, cytological analysis of pericardial fluid often reveals reactive mesothelial cells, necessitating histopathological examination for a definitive diagnosis[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. CT imaging may demonstrate pleural nodularity, pericardial thickening, or intrathoracic lymphadenopathy, potentially supporting a diagnosis of mesothelioma[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, fine-needle aspiration cytology and histopathology remain critical for confirmation[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherapeutic management of pericardial mesothelioma is predominantly palliative, aiming to alleviate symptoms and improve quality of life. Subtotal pericardiectomy is commonly performed to prevent recurrent cardiac tamponade, providing short-term clinical benefit [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Systemic chemotherapy protocols, including carboplatin or doxorubicin-based regimens, have been investigated in selected cases, though their therapeutic efficacy remains uncertain. Intracavitary chemotherapy has shown promise in delaying effusion recurrence but has not demonstrated a clear survival advantage [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Reported median survival intervals demonstrate significant variability, ranging from 74 to 366 days, depending upon the therapeutic approaches implemented[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough the prognosis for pericardial mesothelioma is generally poor, the present case report describes a canine patient who survived for more than 12 months through proactive effusion management, pericardiectomy, and comprehensive supportive care. This case underscores the clinical significance of consistent monitoring protocols and multimodal therapeutic approaches. By presenting a detailed analysis of the clinical presentation, therapeutic interventions, and outcome measures, this report aims to provide valuable guidance for veterinary practitioners managing similar cases, emphasizing the significance of early intervention and multimodal treatment strategies in optimizing patient outcomes.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eA 7-year-old spayed female Pomeranian, weighing 4.58 kg, presented with acute-onset respiratory distress, unproductive cough, and occasional gagging, persisting for approximately 24 hours (Day 0). The patient maintained a normal appetite, though the owner noted concurrent lethargy. Physical examination revealed tachypnea with shallow respiratory patterns and muffled heart sounds on thoracic auscultation. Thoracic radiographs revealed marked cardiomegaly with a vertebral heart score (VHS) of 14.3 and radiographic features suggestive of pleural fluid accumulation (Fig. 1A). Subsequent echocardiography confirmed a moderate pericardial effusion and mild tricuspid valve regurgitation, with no evidence of discrete intracardiac masses (Fig. 1B).\u003c/p\u003e\n\u003cp\u003eInitial clinical pathology on Day 0 identified respiratory acidosis with decreased pH (7.19), elevated PCO₂ (63.9 mmHg), and reduced buffer base (-5.6 mmol/L), while electrolytes remained within reference intervals. Hematologic analysis showed a hematocrit of 51% and a hemoglobin concentration of 15.8 g/dL. Therapeutic intervention comprised ultrasound-guided pericardiocentesis and thoracocentesis, which removed 50 mL of pericardial fluid and 200 mL(Fig. 5) of pleural fluid, respectively, and led to rapid clinical improvement and resolution of respiratory distress. The patient was subsequently treated with pimobendan (0.3 mg/kg orally every 12 hours), furosemide (1 mg/kg orally every 12 hours), pentoxifylline (20 mg/kg orally every 12 hours), and metronidazole (10 mg/kg orally every 12 hours) to prevent effusion recurrence and mitigate secondary pathophysiological processes.\u003c/p\u003e\n\u003cp\u003eA follow-up echocardiographic assessment on Day 3 identified mild mitral regurgitation (mitral regurgitation pressure gradient 143.8 mmHg) and mild ventricular enlargement (left ventricular internal dimension in diastole normalized 1.45, left ventricular internal dimension in systole 14.71 mm). These findings were consistent with stage B1 myxomatous mitral valve degeneration and stage 2 left ventricular diastolic dysfunction. The examination did not identify discrete intracardiac masses, and minimal residual pleural fluid was noted. The attending clinician diagnosed idiopathic pericardial effusion, although infiltrative cardiac neoplasia remained a differential diagnosis that could not be definitively excluded.\u003c/p\u003e\n\u003cp\u003eThe patient maintained clinical stability for approximately nine months before presenting with recurrent respiratory difficulties on Day 275. A thoracic X-ray demonstrated persistent cardiomegaly (VHS 12.2), though respiratory parameters improved during hospitalization. On Day 276, echocardiographic evaluation confirmed recurrent pericardial fluid accumulation necessitating therapeutic drainage of 90 mL. Clinicopathologic evaluation showed mild respiratory acidosis (pH 7.33, PCO₂ 45.8 mmHg), elevated acute phase protein response (C-reactive protein 45 mg/L), and moderate thrombocytopenia (platelet count 148 \u0026times; 10⁹/L).\u003c/p\u003e\n\u003cp\u003eCytomorphologic assessment of the pericardial fluid revealed hemorrhagic effusion with mesothelial cell populations and elevated protein concentration (4.0 g/dL), but no definitive neoplastic cellular criteria. Serum biochemical analysis showed that hepatic and renal parameters were within reference intervals.\u003c/p\u003e\n\u003cp\u003eBetween Days 276 and 520, the patient required progressively more frequent pericardiocentesis interventions, yielding drainage volumes ranging from 67 mL to 240 mL (Fig. 5). The intervals between procedures were shortened from monthly to biweekly. Adjunctive pharmacologic management comprised tranexamic acid (10 mg/kg orally every 12 hours), metronidazole (10 mg/kg orally every 12 hours), pentoxifylline (20 mg/kg orally every 12 hours), and famotidine (0.5 mg/kg orally every 12 hours), although effusion recurrence persisted.\u003c/p\u003e\n\u003cp\u003eCT scan was performed to investigate what was causing the persistent pericardial effusion and to inform potential surgical options. The CT showed pericardial wall thickening, regional lymphadenopathy, and nodular lesions within the mediastinum (Fig. 2). Following the CT scan, pericardiectomy was performed for diagnostic and therapeutic purposes, and a thoracic port was placed to manage pleural effusion (Fig. 4). Cytological analysis of the pericardial fluid (Fig. 3A) identified clusters of mesothelial cells exhibiting moderate nuclear anisokaryosis, finely granular chromatin, and abundant eosinophilic cytoplasm. Scattered erythrophagocytic macrophages and mild neutrophilic infiltration were also observed. Although atypical mesothelial cells raised suspicion for a neoplastic process, definitive cytological criteria for malignancy and invasive behavior were not conclusively observed, underscoring the need for histopathological confirmation. Histopathological examination of the pericardial tissues (Fig. 3C, 3D) revealed neoplastic mesothelial cells forming papillary and glandular structures supported by fibrovascular stroma. The tumor cells displayed prominent nucleoli, moderate nuclear pleomorphism, and abundant eosinophilic cytoplasm. Occasional mitotic figures were observed, and infiltration into underlying connective tissue was also seen (Fig. 3D, arrows). These findings confirmed a diagnosis of malignant pericardial mesothelioma.\u003c/p\u003e\n\u003cp\u003eDespite undergoing subtotal pericardiectomy and concurrent placement of a thoracic drainage port, the pleural effusion recurred progressively from Day 540, necessitating regular drainage via the previously implanted thoracic port. Drainage volumes per session ranged from 70 to 240 mL, with intervals initially between seven and 10 days, which progressively shortened over time(Fig. 5). Cytological analysis of the drained pleural fluid revealed moderate cellularity (white blood cell (WBC) count of 10.21 \u0026times; 10\u0026sup3;/\u0026mu;L) and elevated protein concentration (4.0 g/dL), primarily comprising atypical mesothelial cells with moderate nuclear pleomorphism, fine chromatin, and abundant eosinophilic cytoplasm (Fig. 3B).\u003c/p\u003e\n\u003cp\u003eAlthough these cytological findings alone were insufficient to definitively differentiate malignant mesothelioma from reactive mesothelial proliferation, subsequent histopathological evaluation of the pericardium confirmed malignant features, including the invasion of neoplastic mesothelial cells into adjacent connective tissue. These findings corroborated the diagnosis of malignant pericardial mesothelioma.\u003c/p\u003e\n\u003cp\u003eBecause of ongoing clinical deterioration, oral prednisolone was initiated on Day 620 at a dose of 0.5 mg/kg daily, which was subsequently increased to 1 mg/kg twice daily. The initial response to prednisolone therapy was favorable, temporarily extending intervals between fluid drainage procedures. However, by Day 626, thoracic drainage was required every 1\u0026ndash;2 days, with fluid removal volumes ranging from 80 to 120 mL(Fig. 5). The patient\u0026rsquo;s body weight fluctuated between 5.88 kg and 6.02 kg during this period. Despite intensive supportive care and repeated thoracic fluid drainage, the patient\u0026rsquo;s clinical condition progressively worsened. On Day 627, scheduled thoracic fluid drainage was deferred due to the patient's severely compromised condition, and the patient subsequently succumbed to respiratory arrest on Day 628. The overall survival was approximately 21 months (628 days) following the initial presentation of pericardial effusion.\u003c/p\u003e\n\u003cp\u003eCT images revealing pericardial thickening, regional lymphadenopathy, and nodular changes in the mediastinum, consistent with malignant pericardial mesothelioma.\u003c/p\u003e"},{"header":"Discussion and Conclusions","content":"\u003cp\u003eThis case report describes a rare instance of prolonged survival (21 months) in a dog diagnosed with malignant pericardial mesothelioma, managed without chemotherapy. This outcome emphasizes the critical role of systematic pericardial and pleural fluid management, subtotal pericardiectomy, and supportive therapies in optimizing survival and maintaining quality of life. Previous studies have documented median survival times (MST) for canine malignant pericardial mesothelioma ranging from 74 to 366 days, depending on the treatment approach[1, 2]. While surgical intervention and adjunctive therapies have been associated with extended survival, overall prognosis remains guarded, with only 22% of affected dogs surviving beyond one year 1,8]. The 21-month survival observed in this case underscores the potential benefits of proactive medical and surgical management in prolonging survival and improving quality of life.\u003c/p\u003e\n\u003cp\u003eEstablishing a definitive diagnosis was initially challenging because of the non-specific clinical presentation and inconclusive cytological findings. Thoracic radiographs, echocardiography, and CT identified pericardial thickening and pleural effusion but missed the discrete intracardiac masses, complicating the diagnostic process. These findings align with previous reports describing the diagnostic challenges posed by the infiltrative and diffuse nature of canine mesothelioma[1, 11]. Cytological evaluation of pericardial and pleural fluid (Fig. 3A, 3B) revealed atypical mesothelial cells with anisokaryosis and occasional nucleoli, but definitive malignant characteristics were absent. Given the inherent limitations of cytology in differentiating reactive mesothelial proliferation from neoplastic transformation, histopathological examination was necessary for a conclusive diagnosis.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHistopathological analysis of the excised pericardium confirmed malignant pericardial mesothelioma, characterized by papillary and glandular proliferations of mesothelial cells displaying moderate nuclear pleomorphism, abundant eosinophilic cytoplasm, prominent nucleoli, and occasional mitotic figures, with invasion into adjacent connective tissues (Fig. 3C, 3D), consistent with previously described histologic features of canine pericardial mesothelioma[1, 12, 13]. Although cytological analysis of pericardial and pleural fluid identified atypical mesothelial cells, the findings lacked definitive features of malignancy. This underscores the limited sensitivity and specificity of cytology in detecting pericardial mesothelioma and highlights the importance of histopathological evaluation for definitive diagnosis[1, 2, 12, 14].\u003c/p\u003e\n\u003cp\u003eIn this case, systemic chemotherapy was not undertaken; instead, therapeutic interventions included subtotal pericardiectomy and concurrent thoracic port placement. Subtotal pericardiectomy alleviated recurrent cardiac tamponade, a common complication of pericardial mesothelioma, thereby improving cardiac function and clinical status [5]. Additionally, the thoracic port facilitated the long-term management of recurrent pleural effusion, contributing significantly to the patient’s clinical stability and quality of life.\u003c/p\u003e\n\u003cp\u003eSeveral prognostic factors potentially contributed to the extended survival time observed in this case. Early recognition of clinical signs and immediate therapeutic interventions likely prevented severe cardiac dysfunction and secondary organ impairment. Additionally, a structured follow-up protocol involving consistent clinical evaluations and fluid management facilitated timely interventions that helped maintain clinical stability. Another essential factor was the high level of owner compliance with the therapeutic regimen, enabling effective long-term management. Finally, the patient's relatively young age at diagnosis (7 years) and lack of significant concurrent conditions likely improved tolerance to repeated invasive procedures and physiological resilience, further supporting prolonged survival.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe progression from primary pericardial involvement to subsequent pleural effusion reflects a characteristic pattern of malignant mesothelioma dissemination. Typically, mesothelioma originates as a diffuse neoplastic transformation of mesothelial cells lining the pericardium, spreading insidiously into adjacent structures rather than forming clearly defined masses[11, 15, 16]. This infiltrative growth pattern accounts for the initial diagnostic challenges and the absence of discrete masses on imaging. A pleural effusion developing after pericardiectomy likely represents a direct extension of the neoplastic process to the pleural cavity, consistent with the locally aggressive nature of mesothelioma[17]. The post-pericardiectomy shift from predominantly pericardial to pleural effusion may be explained by the removal of the pericardial barrier, which reduced resistance and allowed fluid to accumulate preferentially in the pleural space[17, 18]. This pattern of disease progression highlights the importance of viewing pericardial and pleural spaces as interconnected in mesothelioma cases, with implications for both diagnostic approaches and therapeutic interventions[19].\u003c/p\u003e\n\u003cp\u003eThroughout the patient's clinical course, a gradual increase in body weight was observed, from 4.58 kg to 6.02 kg over the follow-up period. Such sustained weight gain, despite the underlying malignancy and repeated therapeutic interventions, is a positive prognostic factor, indicating effective symptom control and adequate nutritional support[20, 21]. Previous studies have suggested that maintaining or improving body weight and body condition score (BCS) in dogs with chronic or neoplastic conditions correlates positively with prolonged survival and enhanced quality of life[20, 21]. Conversely, weight loss represents a negative prognostic factor, particularly in patients with chronic disorders including cardiac disease and neoplastic conditions[20, 22]. Moreover, long-term surveillance studies of animals with pericardial fluid accumulation suggest that maintaining body condition correlates with longer overall survival[17]. The association between stable body weight and survival appears multifaceted. For example, stable body weight is indicative of effective control of disease-associated clinical signs including nausea, discomfort, and respiratory compromise[23]. Additionally, stable body weight suggests the preservation of muscle tissue, supporting systemic physiological processes and potentially enhancing resilience to repeated interventions. The absence of cancer-associated cachexia in this patient, despite histologically confirmed malignancy, may reflect the localization of the neoplastic process due to aggressive management[24]. In light of these findings, we recommend methodical nutritional evaluation, consistent body weight monitoring, and client education regarding dietary management as essential elements of comprehensive long-term care protocols for comparable cases. These nutritional considerations may significantly influence therapeutic outcomes in patients with chronic life-limiting disorders.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis single-case report has several limitations, including its retrospective design and the inherent constraints of individual case documentation. Additionally, as chemotherapeutic intervention was not implemented, definitive comparisons between chemotherapy and supportive management cannot be established. Notwithstanding these limitations, our observations can provide valuable clinical perspectives for managing similar cases, particularly emphasizing that comprehensive effusion control and appropriate surgical management alone can significantly extend overall survival.\u003c/p\u003e\n\u003cp\u003eClinical recommendations derived from this case include a sequential diagnostic protocol beginning with non-invasive or minimally invasive techniques, such as thoracic imaging, cardiac ultrasonography, and fluid analysis. When initial diagnostic results are inconclusive, other imaging modalities (e.g., CT) and tissue sampling should be pursued for accurate diagnosis and treatment planning. Monitoring frequency should be adjusted according to effusion recurrence patterns. For this patient, evaluations every two weeks were initially adequate, with subsequent transition to more frequent assessments (weekly, or more often) as their condition progressed. Bespoke monitoring protocols can optimize the balance between effective clinical surveillance and client adherence. Prompt consideration of subtotal pericardiectomy is indicated for cases with recurrent effusion unresponsive to medical therapy, as this intervention both reduces cardiac tamponade risk and provides diagnostic tissue specimens. In patients experiencing rapid pleural fluid reaccumulation, placing an indwelling thoracic port should be considered, as it facilitates efficient fluid removal while reducing patient anxiety and the need for sedation or anesthesia.\u003c/p\u003e\n\u003cp\u003eFurther investigation is necessary to evaluate the comparative effectiveness of various therapeutic strategies, including chemotherapy, surgical interventions, and palliative care, in canine pericardial mesothelioma. Multi-institutional studies examining survival outcomes across different treatment approaches would provide valuable data to enhance prognostic accuracy and develop evidence-based clinical guidelines.\u003c/p\u003e\n\u003cp\u003eThis case described a dog with pericardial mesothelioma that survived for 21 months without chemotherapy. The treatment plan involved sequential effusion drainage, subtotal pericardiectomy, and thoracic port implantation. Our findings suggest that survival can be prolonged without chemotherapy, which may be important in clinical scenarios when the owners refuse chemotherapy or it is considered unsuitable. Further validation of these observations through larger case series would allow refinement of protocols.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eBCS: Body Condition Score\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;CHF: Congestive Heart Failure\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;CT: Computed Tomography\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;VHS: Vertebral Heart Score\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;WBC: White Blood Cell\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;PCO₂: Partial Pressure of Carbon Dioxide\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;MST: Median Survival Time\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors extend their sincere gratitude to the veterinary staff for their dedicated care and technical support during the dog\u0026apos;s treatment and hospitalization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003cbr\u003e\u003c/strong\u003eDK and SGP summarized the data and drafted the manuscript. DK, SGP, JSM, and ISO managed clinical treatment and provided patient care. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003cbr\u003e\u003c/strong\u003eThis study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003cbr\u003e\u003c/strong\u003eAll datasets are available in the main manuscript\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003cbr\u003e\u003c/strong\u003eThe patient was treated at the owner\u0026apos;s request, with informed consent for the treatment process. Clinical data were collected throughout the course of treatment, and written consent was obtained from the owner for the use of medical data for educational and research purposes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003cbr\u003e\u003c/strong\u003eWritten consent for publication was obtained from the dog\u0026rsquo;s owner. All identifying information was excluded, and all images used in the manuscript were obtained during the diagnostic and treatment process with the owner\u0026apos;s permission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003cbr\u003e\u003c/strong\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMoberg HL, Gramer I, Schofield I, Blackwood L, Killick D, Priestnall SL, et al. Clinical presentation, treatment and outcome of canine malignant mesothelioma: A retrospective study of 34 cases. Vet Comp Oncol. 2022;20:304\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLajoinie M, Chavalle T, Floch F, Sayag D, Lanore D, Ponce F, et al. Outcome of dogs treated with chemotherapy for mesothelioma: A retrospective clinical study on 40 cases and a literature review. Vet Comp Oncol. 2022;20:825\u0026ndash;35.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStepien RL, Whitley NT, Dubielzig RR. Idiopathic or mesothelioma-related pericardial effusion: Clinical findings and survival in 17 dogs studied retrospectively. J Small Anim Pract. 2000;41:342\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGlickman LT, Domanski LM, Maguire TG, Dubielzig RR, Churg A. Mesothelioma in pet dogs associated with exposure of their owners to asbestos. Environ Res. 1983;32:305\u0026ndash;13.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMachida N, Tanaka R, Takemura N, Fujii Y, Ueno A, Mitsumori K. Development of pericardial mesothelioma in golden retrievers with a long-term history of idiopathic haemorrhagic pericardial effusion. J Comp Pathol. 2004;131:166\u0026ndash;75.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eScheuermann LM, Gordon-Evans WJ, Nault AJ. Systematic review of the treatment options for pericardial effusions in dogs. Vet Surg. 2021;50:20\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRivera PA, Borgarelli M. Cardiovascular images: constrictive pericarditis and tricavitary effusion in a dog with pericardial mesothelioma. J Vet Cardiol. 2020;32:55\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThrall DE, Goldschmidt MH. Mesothelioma in the Dog: Six Case Reports. Vet Radiol. 1978;19:107\u0026ndash;15.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMin JH, Yoon J, Son S, Song WJ, Lee S, Yun Y, et al. A Rare Case of Canine Pericardial Malignant Mesothelioma: Clinicopathologic Findings, Diagnostic Investigations, and Clinical Course with Epirubicin Treatment. J Vet Clin. 2024;41:170\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNabeta R, Kanaya A, Elbadawy M, Usui T, Furuya T, Suzuki K et al. Chemosensitivity of three patient-derived primary cultures of canine pericardial mesothelioma by single-agent and combination treatment. Front Vet Sci. 2023;10.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRivera PA, Borgarelli M. Cardiovascular images: constrictive pericarditis and tricavitary effusion in a dog with pericardial mesothelioma. J Vet Cardiol. 2020;32:55\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNabeta R, Kanaya A, Elbadawy M, Usui T, Furuya T, Suzuki K et al. Chemosensitivity of three patient-derived primary cultures of canine pericardial mesothelioma by single-agent and combination treatment. Front Vet Sci. 2023;10.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTurk JR, Ikede B 0, Zubaidy A, Gill CW. References Request reprints from Pericardial Mesothelioma with Cardiac Tamponade in a Dog. Marcel Dekker; 1976.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMorini M, Bettini G, Morandi F, Burdisso R, Marcato PS. Deciduoid Peritoneal Mesothelioma in a Dog.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eClosa JM, Font A, Mascort J. Pericardial mesothelioma in a dog: Long-term survival after pericardiectomy in combination with chemotherapy. J Small Anim Pract. 1999;40:383\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrower A, Herold LV, Kirby BM. Canine Cardiac Mesothelioma with Granular Cell Morphology. 2006.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStafford Johnson M, Martin M, Binns S, Day MJ. A retrospective study of clinical findings, treatment and outcome in 143 dogs with pericardial effusion. J Small Anim Pract. 2004;45:546\u0026ndash;52.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDunning D, Monnet E, Orton EC, Salman MD. Analysis of prognostic indicators for dogs with pericardial effusion: 46 cases (1985\u0026ndash;1996). J Am Vet Med Assoc. 1998;212:1276\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWithrow SJ, Vail DM, Page R. Withrow and MacEwen\u0026rsquo;s Small Animal Clinical Oncology. Elsevier Health Sciences; 2012.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMichel KE, Sorenmo K, Shofer FS. Evaluation of body condition and weight loss in dogs presented to a veterinary oncology service. J Vet Intern Med. 2004;18:692\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaker KE, Remillard RL. Critical care nutrition and enteral-assisted feeding. Small Anim Clin Nutr. 2010;5:441\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHubbard WN, Fish DR, McBrien DJ. The use of impedance cardiography in heart failure. Int J Cardiol. 1986;12:71\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnthony RM, Amundson MD, Brejda J, Becvarova I. Acceptance of a Novel, Highly Palatable, Calorically Dense, and Nutritionally Complete Diet in Dogs with Benign and Malignant Tumors. Vet Sci. 2023;10.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFreeman LM. Cachexia and sarcopenia: Emerging syndromes of importance in dogs and cats. J Vet Intern Med. 2012;26:3\u0026ndash;17.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6302384/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6302384/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePericardial mesothelioma is an uncommon and aggressive neoplasm in dogs, typically associated with poor prognosis and limited therapeutic options. Although chemotherapy is frequently used, there is a scarcity of literature describing effective management strategies without chemotherapeutic intervention. This case is reported due to its rarity and the exceptionally long-term survival achieved through non-chemotherapeutic, multimodal management.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCase presentation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA 7-year-old spayed female Pomeranian presented with acute respiratory distress caused by pericardial effusion. The initial management involved pericardiocentesis and medical therapy, but recurrence of effusion necessitated surgical intervention. Subtotal pericardiectomy was performed, and malignant pericardial mesothelioma was confirmed histopathologically. A thoracic port was implanted postoperatively for ongoing effusion management. Remarkably, the patient remained clinically stable and maintained a good quality of life for 21 months (628 days) without chemotherapy, supported by regular monitoring and comprehensive symptomatic care.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis case underscores the clinical importance of individualized, multimodal therapeutic approaches in the management of canine pericardial mesothelioma. It highlights that prolonged survival can be achieved through aggressive effusion control and surgical interventions, even in the absence of systemic chemotherapy. The findings provide valuable insights and potential implications for veterinary clinicians handling similar challenging neoplastic cases.\u003c/p\u003e","manuscriptTitle":"Clinical Course and Extended Survival in a Canine Patient with Pericardial Mesothelioma Managed Without Chemotherapeutic Intervention","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-20 06:46:38","doi":"10.21203/rs.3.rs-6302384/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"774e3b83-57db-414c-9f96-9b1bf50fff01","owner":[],"postedDate":"May 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-01T06:38:54+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-20 06:46:38","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6302384","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6302384","identity":"rs-6302384","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}