Primary Intramuscular T-cell Lymphoma with MUM-1 Expression in a Dog

Primary Intramuscular T-cell Lymphoma with MUM-1 Expression in a Dog | 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 Primary Intramuscular T-cell Lymphoma with MUM-1 Expression in a Dog Megan Gutwillig, Paula Schaffer, Paula Yoon, Kate Vickery This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8929002/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Background : In both humans and veterinary species, primary intramuscular lymphoma is a rarely reported condition. Limited literature available shows that these tumors are often multifocal, with clinical signs often including limb edema and swelling, and lameness. Signs are typically acute and rapidly progressive. Case Presentation : A 10-year-old castrated male dog with multifocal intramuscular masses was diagnosed as T-cell Lymphoma with aberrant MUM-1 expression. He presented due to rapidly progressive right hindlimb edema. The diagnosis was difficult to achieve in this case due to an unusual pattern of expression of surface markers. A combination of contrast CT, cytology, histopathology, immunohistochemistry, and PARR were necessary to achieve a final diagnosis. The dog had an initial rapid response to doxorubicin, but progressive disease was noted shortly after the third dose was administered. He was then treated with rescue chemotherapy protocols and focal radiation therapy. Despite these aggressive therapies, his disease was further progressive and due to poor quality of life humane euthanasia was pursued 63 days after initial presentation. Conclusions : Intramuscular lymphoma appears to be an aggressive subtype of lymphoma. Diagnosis can be difficult in these cases, and a multi-modal approach is often necessary. While these patients can respond well to chemotherapy and radiation therapy, the response is often short-lived, and prognosis remains guarded for these dogs. Intramuscular lymphoma T-cell MUM-1 Figures Figure 1 Figure 2 Figure 3 Figure 4 BACKGROUND Primary intramuscular lymphoma is rarely reported in dogs. In people, primary intramuscular lymphoma represents less than 1% of extranodal lymphoma cases. Limb swelling and muscle pain are the most common symptoms in people (1–3). These cases have a diverse presentation with some reported cases occurring in the muscles of the limbs and pelvis (1–3). Locations of these lesions in people are varied with reports of the sartorius, psoas, gastrocnemius and soleus muscles, and in two cases were reported to be B-cell in origin (1–3). To our knowledge, there are three case reports of confirmed or presumed primary muscular lymphoma in dogs. In one case, a 16-month-old Bullmastiff presented for an acute onset of right pelvic limb edema and cytology was most consistent with lymphoma with atypical vacuolation noted (4). This dog developed numerous skin lesions and a few days later became obstipated due to lateral deviation of the rectum/anus. At this time humane euthanasia was elected by his owners. A bone marrow aspirate was performed immediately after death with no evidence of neoplasia present, but multifocal muscular masses were identified throughout his body on necropsy. Immunohistochemistry (IHC) was negative for CD3 (T cell marker) and additional IHC was not performed therefore a definitive diagnosis of intramuscular lymphoma based on histopathology could not be confirmed. Another case involved an 8-year-old Newfoundland presenting with a large ventral cervical mass, anorexia, and respiratory distress (5). The mass was reported to be approximately 25cm with regional lymphadenopathy. Cytology of the mass was consistent with anaplastic large cell lymphoma and lymph node cytology showed a minor population of neoplastic cells with many immature plasma cells and small lymphocytes present, so it was presumed that the intramuscular mass represented the primary tumor. A modified Cotter protocol (Vincristine 0.75 mg/m2/week for 4 weeks, then every 3 weeks, cyclophosphamide 250 mg/m2 once a month, and prednisolone 1 mg/kg/day for 3 weeks then every other day) was initiated, and a response was noted for 6 weeks. Euthanasia was elected at the time of progression. Necropsy found that the cervical mass infiltrated the musculature of the ventral neck, left forelimb and scapular muscles, and extended cranially to the tongue and laryngeal muscles. Multifocal masses were noted within the gluteal, diaphragmatic, intercostal, and abdominal muscles. The masses were examined and consistent with anaplastic large cell lymphoma, and IHC showed CD3 positivity of the neoplastic cells, confirming a diagnosis of T cell intramuscular lymphoma. The third case report is of a 5-year-old Beagle who presented for a rapidly growing mass of the right shoulder involving the majority of the triceps muscle, with associated lameness of the right forelimb (6). Cytology and histopathology were consistent with large cell lymphoma. Palliative care with steroids, antibiotics, and acetaminophen was pursued. One month later, the dog developed multifocal cutaneous lesions. CT scan of the thorax revealed the previously known large mass associated with the right shoulder but also multifocal lesions in the musculature of the left thorax limb, dorsal neck, body wall, and head. IHC confirmed CD3, PAX5 (B cell marker), and MUM1 (plasma cell marker) positivity, and PCR for antigen receptor rearrangements (PARR) was consistent with a clonal T-cell receptor rearrangement in both the largest muscular mass and cutaneous masses. This dog was euthanized with no further treatment nor necropsy. Given the paucity of information in the literature on this rare form of lymphoma in dogs, we present this case report which to the best of the authors’ knowledge, is the only report to demonstrate tumor response to various chemotherapeutic agents and radiation. CASE PRESENTATION A 10-year-old castrated male mixed breed dog presented to emergency services at Colorado State University (CSU) due to rapid, progressive onset of edema that started along the right hind leg and progressed along the right caudal ventrum. Edema was first noted four days prior to presentation when he was seen by his primary veterinarian for a wellness visit, at which time mild focal edema was noted around the right tarsus. This was initially suspected to be related to a soft tissue injury. He also had an ulcerated cutaneous lesion of the right lateral neck that was initially diagnosed as a focal dermatopathy. A fine needle aspirate (FNA) of this cutaneous lesion was obtained however cytology was non-diagnostic. The tarsal edema rapidly progressed and he was subsequently seen by an emergency clinic that evening. A 4cm x 6cm mass effect in the right inguinal region was identified. Complete blood count (CBC) and chemistry profile was unremarkable and 4Dx (heartworm, Lyme, ehrlichiosis, and anaplasmosis) test was negative. He was discharged from the emergency clinic. Three days later diarrhea developed and he was seen again by the primary care veterinarian. A point of care ultrasound found that the mass in the right inguinal region had grown to 7cm. He was prescribed metronidazole and an anti-inflammatory dose of prednisone. He re-presented the following day for progressive edema of the right hind limb and right inguinal region, at which point he was referred to CSU for further evaluation. About a month prior to this event, he had an episode of hemorrhagic pericardial effusion that was determined to be idiopathic in nature after an echocardiogram found no evidence of a mass effect and an abdominal ultrasound revealed no abnormalities. He had no recurrent pericardial effusion noted since that incident. On presentation to CSU he was noted to have severe pitting edema along his right hind limb and right inguinal region (Figure 1A and 1B). The mass effect in his right inguinal region was not palpable as it was obscured by edema. The previously noted ulcerated cutaneous lesion on his right lateral neck appeared to be healing with an intact scab over the area (Figure 1C). His care was transferred to the oncology service due to a high suspicion for neoplasia. A CT scan of his right hind limb, abdomen, and thorax revealed multifocal isoattenuating, contrast-enhancing, poorly circumscribed intramuscular masses throughout the body. There was also marked soft tissue swelling with fat stranding of the subcutis throughout the body, most notable in the right hindlimb, corresponding to physical exam findings. Angiography ruled out the presence of a thrombus contributing to the edema, and contrast highlighted the presence of these masses, which were subtle prior to contrast delivery. Muscles involved included the left and right semimembranosus, adductor magnus, vastus lateralis, gluteals, the right gracilis and biceps femoris, the thorax and lumbar epaxials, left subscapularis, and right infraspinatus and triceps (Figure 2). Notably there were no masses within the cardia, but there were two small masses noted dorsolateral to the caudal vena cava within the plica vena cava. Additionally, there were two soft tissue nodules adjacent to the right and left ventricular free walls. There was mild lymphadenomegaly of the medial iliac, right internal iliac, and sternal lymph nodes. Ultrasound guided FNA of the masses within the left and right thigh muscles were obtained. On ultrasound, there were poorly defined heterogeneous hypoechoic nodules to masses expanding disrupting the muscle fiber pattern of the hindlimb musculature. These lesions corresponded to the contrast enhancing lesions on same day CT. Cytology was consistent with discrete cell neoplasm. The neoplastic cells were described as numerous individualized round cells with a small to abundant amount of lightly basophilic cytoplasm that often contain many distinct, punctate vacuoles and a single round to indented, centric to paracentric nucleus. Nuclei had stippled chromatin and 1-3 distinct round to oval nucleoli. Atypia was mild to moderate with some of the neoplastic cells having macronucleoli that were approximately the size of an erythrocyte. Given these cytologic features, differentials provided included lymphoma, poorly differentiated embryonal neoplasm such as embryonal rhabdomyosarcoma, extraosseous osteosarcoma, histiocytic sarcoma, and less likely hemangiosarcoma. Clinically, the dog’s edema was rapidly progressive, though he remained hemodynamically stable and non-painful on exam. Based on rapid progression of the edema and lack of a definitive diagnosis from cytology, it was elected to obtain ultrasound guided tru-cut biopsies of the masses in his left thigh musculature. The musculature of the right hind limb was not amendable to biopsy sampling due to the degree of edema. The following day, his edema continued to progress with extension down his right forelimb. Based on clinical progression and after discussing risks and potential complications with the owners, it was elected to move forward with chemotherapy treatment before histopathology results were available. Based on the top cytologic differentials of lymphoma or rhabdomyosarcoma, a dose of L-Asparaginase (L-SPAR) (10,000 IU/m2 SQ) and doxorubicin (DOX) (30 mg/m2 IV) was pursued to relieve his clinical signs and slow the progression of edema. He was discharged to his owners after treatment. His owners reported improvement in the edema 24 hours after treatment and near complete resolution within 72 hours. Histopathology demonstrated high numbers of neoplastic cells infiltrating between myocytes, frequently isolating them from each other (Figure 3A). The neoplastic cells were round to polyglonal with small amounts of amphophilic cytoplasm and large round or oval nuclei ≥2 times the diameter of erythrocytes. There were 25 mitoses noted in 2 high-powered fields. IHC was performed to further discern tumor type. The neoplastic cells were immunonegative for Desmin (a myocyte marker), CD3, CD20 (B cell marker), Pax5, CD204 and Iba1 (both histiocytic markers). Cells were diffusely immunoreactive for vimentin and approximately 75% of cells demonstrated strong nuclear reactivity for Mum-1 (Figure 3B). Based on these results, the masses were suspected to represent a plasma cell tumor. However, PCR for Antigen Receptor Rearrangements (PARR) performed on the histopathology and cytology samples taken from the thigh muscle revealed polyclonal immunoglobulin gene but a clonal T-cell receptor gene, which was discordant with the histopathologic diagnosis of plasma cell tumor. Due to this discordance, additional IHC for CD34 and CD30 was pursued and were both negative, ruling out anaplastic large cell lymphoma. Based on this combination of diagnostic findings, a diagnosis of T-cell Lymphoma with aberrant Mum-1 expression was made. Due to the multiple IHC markers needed to obtain a definitive diagnosis, this diagnosis arrived much later than typical, approximately 31 days after the dog’s first treatment with L-SPAR and DOX. While awaiting a definitive diagnosis and due to the excellent initial response to L-SPAR and DOX, it was elected to continue treatment with single agent DOX intravenous every 3 weeks. Shortly after the third DOX dose, the owners reported a suspected seizure-like event at home. He re-presented to CSU the following day. A new large mass effect at the base of the left ear with associated edema and swelling along the left side of his head was noted, concerning for progressive disease. Cytology of the mass effect showed the same neoplastic cell population as described previously. Given the evidence for progression of disease and suspected central nervous system involvement, his chemotherapy protocol was switched to a Lomustine (70mg/m2 PO every 3 weeks) and L-SPAR (10,000 mg/m2 SQ) combination protocol. His owners sent an update two days after treatment that the new swelling was improving and nearly resolved (Figure 4B), however by eight days after treatment the mass effect had recurred and progressed, surrounding the left eye (Figure 4B). During this time, despite the swelling, he continued to eat well and was only mildly lethargic according to the owners. Nine days after Lomustine treatment, he returned to CSU for evaluation. On exam there was severe swelling and edema around the left eye extending ventrally (Figure 4C). Due to the continued progression and lack of durable response to chemotherapy, the clients elected to proceed with a single fraction of palliative radiation therapy to the left side of the head (6-grey x 1 via manual set-up). He also received one dose of an MVPP protocol (mechlorethamine 3mg/m2 IV, vinblastine 2mg/m2 IV, procarbazine 50mg/m2 PO for 1 week, prednisolone 40 mg/m2 PO for 1 week) protocol. An update from the owner one week later reported improvement of the left sided facial swelling though the ventral edema was reportedly stable. However, eleven days after this treatment, he developed progressive edema along his limbs and ventrum. For the first time since diagnosis, he had trouble rising and was uncomfortable, and his owners elected to proceed with humane euthanasia, 63 days after initial presentation to CSU. A necropsy was not performed. DISCUSSION AND CONCLUSIONS This case report describes the clinical course of a dog with primary intramuscular lymphoma, a rarely reported form of lymphoma. Similar to prior case reports of this disease, the dog described here had an acute presentation of multifocal tumors. Presenting signs included limb swelling, edema, pain associated with the mass effects, and constitutional signs such as hyporexia and lethargy. In our case, cytology did elevate lymphoma as a differential early in the case work up, but histopathology was initially discordant with this diagnosis. Diagnosis typically relies on histopathology with IHC to confirm the diagnosis, and PARR may be utilized to further support a lymphoma diagnosis. When treated, as evidenced in one previously published case report and in the dog described here, these masses can respond to chemotherapy however tend to progress rapidly even with aggressive therapy (5). Previously reported cases documented one presumed B-cell lymphoma and two cases with IHC confirmed T-cell lymphoma (4–6). Interestingly, one case was reported to be CD3 and MUM-1 positive with a clonal T-cell population noted with PARR (6). While the case outlined in this report was negative for CD3 and CD20 with positive MUM-1 expression, the final diagnosis of T-cell Lymphoma with MUM-1 expression was made based on a clonal T-cell receptor population noted on PARR. This highlights the diagnostic challenge that can occur with round cell tumors, and that a multi-modal diagnostic approach utilizing multiple IHC markers and PARR is needed to obtain a definitive diagnosis, likely due to aberrant expression of markers not typically associated with these tumors. Advanced imaging also played a role in determining the extent of disease, particularly the use of contrast enhanced the masses, as they were not visible with non-contrast CT or ultrasound alone. This case represents the longest response to treatment in a dog with primary intramuscular lymphoma at 63 days of overall survival time. To our knowledge, the only other case previously reported that was treated had a reported survival of 6 weeks (6). However, this patient was euthanized when progression occurred after first line therapy, and no rescue protocols were attempted while in our case the owners were willing to continue with further treatment as long as his quality of life was acceptable. This case highlights that this tumor type can respond to single-agent doxorubicin, Lomustine/L-SPAR, and MVPP protocols, though the response to each protocol was short-lived. Radiation therapy in this case reduced significant swelling rapidly, improving the dog’s quality of life, and may play a role in local disease control in other patients. Due to this dog’s rapid progression, monotherapy with DOX was pursued prior to the final diagnosis, and continued due to his response to this therapy. In retrospect knowing the final diagnosis, a CHOP-based protocol likely would have been our first line recommendation. In conclusion, this case report summarizes the extensive diagnostic workup and treatment of a dog with primary intramuscular T-cell lymphoma. The limited literature to date highlights the rarity of this form of lymphoma in dogs. Literature in humans is also very scarce with only a handful of case reports with no consensus available for accurate diagnosis, treatment, and outcome data available. This case highlights that dogs with this diagnosis can respond to systemic chemotherapy and radiation therapy, though this response appears to be short-lived. Diagnosis in these cases can also be challenging, and it should be kept in mind that treatment may need to be pursued prior to final diagnosis. It may also be valuable to expedite cytology and biopsy with immunohistochemical and PARR analysis in suspect cases with multifocal intramuscular masses. Primary intramuscular lymphoma should be considered as a differential in patients with acute presentation of rapid progression of limb edema and multifocal masses. However, conclusions about treatment for these patients would ideally be reached with review of additional cases but given the rarity of this tumor type this will likely be challenging. Abbreviations L-SPAR: L-Asparaginase SQ: Subcutaneous DOX: doxorubicin IV: Intravenous IHC: immunohistochemistry PARR: PCR for antigen receptor rearrangements Declarations Ethics approval and consent to participate: n/a Consent for publication: The patient’s owner was contacted via email on 02DEC25 and provided permission for publication of the included information and photographs of the patient. Availability of data and materials: n/a Competing interests: The authors declare that they have no competing interests Funding: n/a Authors' contributions: MG was the primary author with contributions from the remaining authors including editing and compilation of the figures included. PY provided interpretation of the CT and the included CT images. PS read the histopathology and guided IHC recommendations, and provided the included histopathology images. All authors read and approved the final manuscript. Acknowledgements: The authors would like to thank this patient’s owners for providing permission for publication. They also provided routine updates on his status throughout his treatment, and several of the photos included here are from these updates, used with their permission. References Alexander V, Shenoy R, Korula A, Koshy M. Intramuscular lymphoma: uncommon presentation of Hodgkin’s disease. BMJ Case Rep. 2020 Aug;13(8):e229826. Gao S, Shu H, Yang H. Imaging features of skeletal muscle lymphoma: a case report and literature review. BMC Med Imaging. 2021 Dec;21(1):136. Chew FS, Schellingerhout D, Keel SB. Primary lymphoma of skeletal muscle. Am J Roentgenol. 1999 May;172(5):1370–1370. Harkin K, Kennedy G, Moore W, Schoning P. Skeletal muscle lymphoma in a bullmastiff. J Am Anim Hosp Assoc. 2000 Jan 1;36(1):63–6. Thuilliez C, Watrelot-Virieux D, Chanut F, Fournel-Fleury C, Ponce F, Marchal T. Presumed Primary Muscular Lymphoma in a Dog. J Vet Diagn Invest. 2008 Nov;20(6):824–6 Lopes MG, Marchesi F, Haining H, Morris JS. Primary multifocal muscular T-cell lymphoma with cutaneous involvement in a dog: A case report and review of the literature. Vet Clin Pathol. 2021 Dec 1;50(4):584–8. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 12 Mar, 2026 Reviews received at journal 08 Mar, 2026 Reviews received at journal 05 Mar, 2026 Reviews received at journal 05 Mar, 2026 Reviewers agreed at journal 25 Feb, 2026 Reviewers agreed at journal 24 Feb, 2026 Reviewers agreed at journal 24 Feb, 2026 Reviewers invited by journal 23 Feb, 2026 Editor assigned by journal 23 Feb, 2026 Submission checks completed at journal 23 Feb, 2026 First submitted to journal 20 Feb, 2026 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-8929002","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":596975874,"identity":"5cf3d597-49d9-4f76-beac-b42e0fe73728","order_by":0,"name":"Megan Gutwillig","email":"data:image/png;base64,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","orcid":"","institution":"Colorado State University","correspondingAuthor":true,"prefix":"","firstName":"Megan","middleName":"","lastName":"Gutwillig","suffix":""},{"id":596975875,"identity":"42d01a9f-9712-472e-ac18-9d120b6012f6","order_by":1,"name":"Paula Schaffer","email":"","orcid":"","institution":"Colorado State University","correspondingAuthor":false,"prefix":"","firstName":"Paula","middleName":"","lastName":"Schaffer","suffix":""},{"id":596975876,"identity":"b1ac4f4f-d7e4-49fc-beea-5c429bb167a3","order_by":2,"name":"Paula Yoon","email":"","orcid":"","institution":"Colorado State University","correspondingAuthor":false,"prefix":"","firstName":"Paula","middleName":"","lastName":"Yoon","suffix":""},{"id":596975877,"identity":"5d27bfc6-5c09-463f-9ec3-6d6b7c1508a3","order_by":3,"name":"Kate Vickery","email":"","orcid":"","institution":"Colorado State University","correspondingAuthor":false,"prefix":"","firstName":"Kate","middleName":"","lastName":"Vickery","suffix":""}],"badges":[],"createdAt":"2026-02-20 20:53:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8929002/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8929002/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103576167,"identity":"94ea0631-d127-42dd-8610-fd5f4ad27783","added_by":"auto","created_at":"2026-02-27 09:13:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":689069,"visible":true,"origin":"","legend":"\u003cp\u003ePhysical exam findings on presentation to CSU Oncology Service\u003c/p\u003e\n\u003cp\u003eA/B: Edema along right hind limb and ventral abdomen.\u003c/p\u003e\n\u003cp\u003eC: Dermal lesion on right lateral neck.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8929002/v1/0fecd3a14f5594c147d1359a.png"},{"id":104399077,"identity":"f445fba1-16b5-49b2-a4d0-32abd14262a0","added_by":"auto","created_at":"2026-03-11 12:04:41","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":274491,"visible":true,"origin":"","legend":"\u003cp\u003eCT findings\u003c/p\u003e\n\u003cp\u003eA/B: Pre and post-contrast transverse CT of the hindlimb musculature.\u003c/p\u003e\n\u003cp\u003eAsymmetry of the gluteal musculature, with increased size of the right gluteal musculature and regional subcutaneous fat stranding. On the post contrast series, there is ill-defined multifocal lesions that are strongly and heterogeneously contrast enhancing, and not visible on the pre contrast series.\u003c/p\u003e\n\u003cp\u003eC: Post-contrast dorsal CT.\u003c/p\u003e\n\u003cp\u003eMultifocal strongly heterogeneously contrast enhancing nodules to masses of the proximal hindlimb musculature bilaterally.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8929002/v1/3217ff770c86356d4a75ce16.png"},{"id":103576165,"identity":"9a167535-3950-4b04-9e60-cd8e7b698949","added_by":"auto","created_at":"2026-02-27 09:13:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":712711,"visible":true,"origin":"","legend":"\u003cp\u003eHistopathology results from left thigh mass\u003c/p\u003e\n\u003cp\u003eA: Neoplastic cells form densely cellular sheets amongst myocytes (M). \u0026nbsp;Multiple mitoses are evident in this field (arrowheads). \u0026nbsp;Hematoxylin and eosin.\u003c/p\u003e\n\u003cp\u003eB: \u0026nbsp;Neoplastic cells demonstrate strong nuclear immunoreactivity for Mum-1. Immunohistochemistry.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8929002/v1/34464192f0f16c088e0b743c.png"},{"id":103576168,"identity":"94f7754f-3f07-44d8-88a9-31b1e1cc219e","added_by":"auto","created_at":"2026-02-27 09:13:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":920774,"visible":true,"origin":"","legend":"\u003cp\u003ePhysical exam findings tracking progression following doxorubucin therapy.\u003c/p\u003e\n\u003cp\u003eA: Facial swelling noted by owners 11 days after his third dose of doxorubicin.\u003c/p\u003e\n\u003cp\u003eB: Partial resolution 2 days after treatment with CCNU/L-SPAR.\u003c/p\u003e\n\u003cp\u003eC: Rapid progression noted 9 days after CCNU/L-SPAR dose.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8929002/v1/cc8ee3b34ec6d2d80d489933.png"},{"id":104407400,"identity":"5d767179-af04-4cd2-a997-8a13a1994229","added_by":"auto","created_at":"2026-03-11 12:37:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3714334,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8929002/v1/1db66bf5-e293-4599-84f0-31ee3ada8bbf.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Primary Intramuscular T-cell Lymphoma with MUM-1 Expression in a Dog","fulltext":[{"header":"BACKGROUND","content":"\u003cp\u003ePrimary intramuscular lymphoma is rarely reported in dogs. In people, primary intramuscular lymphoma represents less than 1% of extranodal lymphoma cases. Limb swelling and muscle pain are the most common symptoms in people (1\u0026ndash;3). These cases have a diverse presentation with some reported cases occurring in the muscles of the limbs and pelvis (1\u0026ndash;3). Locations of these lesions in people are varied with reports of the sartorius, psoas, gastrocnemius and soleus muscles, and in two cases were reported to be B-cell in origin (1\u0026ndash;3).\u003c/p\u003e \u003cp\u003eTo our knowledge, there are three case reports of confirmed or presumed primary muscular lymphoma in dogs. In one case, a 16-month-old Bullmastiff presented for an acute onset of right pelvic limb edema and cytology was most consistent with lymphoma with atypical vacuolation noted (4). This dog developed numerous skin lesions and a few days later became obstipated due to lateral deviation of the rectum/anus. At this time humane euthanasia was elected by his owners. A bone marrow aspirate was performed immediately after death with no evidence of neoplasia present, but multifocal muscular masses were identified throughout his body on necropsy. Immunohistochemistry (IHC) was negative for CD3 (T cell marker) and additional IHC was not performed therefore a definitive diagnosis of intramuscular lymphoma based on histopathology could not be confirmed.\u003c/p\u003e \u003cp\u003eAnother case involved an 8-year-old Newfoundland presenting with a large ventral cervical mass, anorexia, and respiratory distress (5). The mass was reported to be approximately 25cm with regional lymphadenopathy. Cytology of the mass was consistent with anaplastic large cell lymphoma and lymph node cytology showed a minor population of neoplastic cells with many immature plasma cells and small lymphocytes present, so it was presumed that the intramuscular mass represented the primary tumor. A modified Cotter protocol (Vincristine 0.75 mg/m2/week for 4 weeks, then every 3 weeks, cyclophosphamide 250 mg/m2 once a month, and prednisolone 1 mg/kg/day for 3 weeks then every other day) was initiated, and a response was noted for 6 weeks. Euthanasia was elected at the time of progression. Necropsy found that the cervical mass infiltrated the musculature of the ventral neck, left forelimb and scapular muscles, and extended cranially to the tongue and laryngeal muscles. Multifocal masses were noted within the gluteal, diaphragmatic, intercostal, and abdominal muscles. The masses were examined and consistent with anaplastic large cell lymphoma, and IHC showed CD3 positivity of the neoplastic cells, confirming a diagnosis of T cell intramuscular lymphoma.\u003c/p\u003e \u003cp\u003eThe third case report is of a 5-year-old Beagle who presented for a rapidly growing mass of the right shoulder involving the majority of the triceps muscle, with associated lameness of the right forelimb (6). Cytology and histopathology were consistent with large cell lymphoma. Palliative care with steroids, antibiotics, and acetaminophen was pursued. One month later, the dog developed multifocal cutaneous lesions. CT scan of the thorax revealed the previously known large mass associated with the right shoulder but also multifocal lesions in the musculature of the left thorax limb, dorsal neck, body wall, and head. IHC confirmed CD3, PAX5 (B cell marker), and MUM1 (plasma cell marker) positivity, and PCR for antigen receptor rearrangements (PARR) was consistent with a clonal T-cell receptor rearrangement in both the largest muscular mass and cutaneous masses. This dog was euthanized with no further treatment nor necropsy.\u003c/p\u003e \u003cp\u003eGiven the paucity of information in the literature on this rare form of lymphoma in dogs, we present this case report which to the best of the authors\u0026rsquo; knowledge, is the only report to demonstrate tumor response to various chemotherapeutic agents and radiation.\u003c/p\u003e"},{"header":"CASE PRESENTATION","content":"\u003cp\u003eA 10-year-old castrated male mixed breed dog presented to emergency services at Colorado State University (CSU) due to rapid, progressive onset of edema that started along the right hind leg and progressed along the right caudal ventrum. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEdema was first noted four days prior to presentation when he was seen by his primary veterinarian for a wellness visit, at which time mild focal edema was noted around the right tarsus. This was initially suspected to be related to a soft tissue injury. He also had an ulcerated cutaneous lesion of the right lateral neck that was initially diagnosed as a focal dermatopathy. A fine needle aspirate (FNA) of this cutaneous lesion was obtained however cytology was non-diagnostic. The tarsal edema rapidly progressed and he was subsequently seen by an emergency clinic that evening. A 4cm x 6cm mass effect in the right inguinal region was identified. Complete blood count (CBC) and chemistry profile was unremarkable and 4Dx (heartworm, Lyme, ehrlichiosis, and anaplasmosis) test was negative. He was discharged from the emergency clinic. Three days later diarrhea developed and he was seen again by the primary care veterinarian. A point of care ultrasound found that the mass in the right inguinal region had grown to 7cm. He was prescribed metronidazole and an anti-inflammatory dose of prednisone. He re-presented the following day for progressive edema of the right hind limb and right inguinal region, at which point he was referred to CSU for further evaluation. About a month prior to this event, he had an episode of hemorrhagic pericardial effusion that was determined to be idiopathic in nature after an echocardiogram found no evidence of a mass effect and an abdominal ultrasound revealed no abnormalities. He had no recurrent pericardial effusion noted since that incident. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOn presentation to CSU he was noted to have severe pitting edema along his right hind limb and right inguinal region (Figure 1A and 1B). The mass effect in his right inguinal region was not palpable as it was obscured by edema. The previously noted ulcerated cutaneous lesion on his right lateral neck appeared to be healing with an intact scab over the area (Figure 1C). His care was transferred to the oncology service due to a high suspicion for neoplasia. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA CT scan of his right hind limb, abdomen, and thorax revealed multifocal isoattenuating, contrast-enhancing, poorly circumscribed intramuscular masses throughout the body. There was also marked soft tissue swelling with fat stranding of the subcutis throughout the body, most notable in the right hindlimb, corresponding to physical exam findings. Angiography ruled out the presence of a thrombus contributing to the edema, and contrast highlighted the presence of these masses, which were subtle prior to contrast delivery. Muscles involved included the left and right semimembranosus, adductor magnus, vastus lateralis, gluteals, the right gracilis and biceps femoris, the thorax and lumbar epaxials, left subscapularis, and right infraspinatus and triceps (Figure 2). Notably there were no masses within the cardia, but there were two small masses noted dorsolateral to the caudal vena cava within the plica vena cava. Additionally, there were two soft tissue nodules adjacent to the right and left ventricular free walls. There was mild lymphadenomegaly of the medial iliac, right internal iliac, and sternal lymph nodes. Ultrasound guided FNA of the masses within the left and right thigh muscles were obtained. On ultrasound, there were poorly defined heterogeneous hypoechoic nodules to masses expanding disrupting the muscle fiber pattern of the hindlimb musculature. These lesions corresponded to the contrast enhancing lesions on same day CT. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCytology was consistent with discrete cell neoplasm. The neoplastic cells were described as numerous individualized round cells with a small to abundant amount of lightly basophilic cytoplasm that often contain many distinct, punctate vacuoles and a single round to indented, centric to paracentric nucleus. Nuclei had stippled chromatin and 1-3 distinct round to oval nucleoli. Atypia was mild to moderate with some of the neoplastic cells having macronucleoli that were approximately the size of an erythrocyte. Given these cytologic features, differentials provided included lymphoma, poorly differentiated embryonal neoplasm such as embryonal rhabdomyosarcoma, extraosseous osteosarcoma, histiocytic sarcoma, and less likely hemangiosarcoma. Clinically, the dog\u0026rsquo;s edema was rapidly progressive, though he remained hemodynamically stable and non-painful on exam. Based on rapid progression of the edema and lack of a definitive diagnosis from cytology, it was elected to obtain ultrasound guided tru-cut biopsies of the masses in his left thigh musculature. The musculature of the right hind limb was not amendable to biopsy sampling due to the degree of edema.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe following day, his edema continued to progress with extension down his right forelimb. Based on clinical progression and after discussing risks and potential complications with the owners, it was elected to move forward with chemotherapy treatment before histopathology results were available. Based on the top cytologic differentials of lymphoma or rhabdomyosarcoma, a dose of L-Asparaginase (L-SPAR) (10,000 IU/m2 SQ) and doxorubicin (DOX) (30 mg/m2 IV) was pursued to relieve his clinical signs and slow the progression of edema. He was discharged to his owners after treatment. His owners reported improvement in the edema 24 hours after treatment and near complete resolution within 72 hours. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHistopathology demonstrated \u0026nbsp;high numbers of neoplastic cells infiltrating between myocytes, frequently isolating them from each other (Figure 3A). The neoplastic cells were round to polyglonal with small amounts of amphophilic cytoplasm and large round or oval nuclei \u0026ge;2 times the diameter of erythrocytes. There were 25 mitoses noted in 2 high-powered fields. IHC was performed to further discern tumor type. The neoplastic cells were immunonegative for Desmin (a myocyte marker), CD3, CD20 (B cell marker), Pax5, CD204 and Iba1 (both histiocytic markers). Cells were diffusely immunoreactive for vimentin and approximately 75% of cells demonstrated strong nuclear reactivity for Mum-1 (Figure 3B). Based on these results, the masses were suspected to represent a plasma cell tumor. However, PCR for Antigen Receptor Rearrangements (PARR) performed on the histopathology and cytology samples taken from the thigh muscle revealed polyclonal immunoglobulin gene but a clonal T-cell receptor gene, which was discordant with the histopathologic diagnosis of plasma cell tumor. Due to this discordance, additional IHC for CD34 and CD30 was pursued and were both negative, ruling out anaplastic large cell lymphoma. Based on this combination of diagnostic findings, a diagnosis of T-cell Lymphoma with aberrant Mum-1 expression was made. Due to the multiple IHC markers needed to obtain a definitive diagnosis, this diagnosis arrived much later than typical, approximately 31 days after the dog\u0026rsquo;s first treatment with L-SPAR and DOX. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWhile awaiting a definitive diagnosis and due to the excellent initial response to L-SPAR and DOX, it was elected to continue treatment with single agent DOX intravenous every 3 weeks. Shortly after the third DOX dose, the owners reported a suspected seizure-like event at home. He re-presented to CSU the following day. A new large mass effect at the base of the left ear with associated edema and swelling along the left side of his head was noted, concerning for progressive disease. Cytology of the mass effect showed the same neoplastic cell population as described previously. Given the evidence for progression of disease and suspected central nervous system involvement, his chemotherapy protocol was switched to a Lomustine (70mg/m2 PO every 3 weeks) and L-SPAR (10,000 mg/m2 SQ) combination protocol. His owners sent an update two days after treatment that the new swelling was improving and nearly resolved (Figure 4B), however by eight days after treatment the mass effect had recurred and progressed, surrounding the left eye (Figure 4B). During this time, despite the swelling, he continued to eat well and was only mildly lethargic according to the owners. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNine days after Lomustine treatment, he returned to CSU for evaluation. On exam there was severe swelling and edema around the left eye extending ventrally (Figure 4C). Due to the continued progression and lack of durable response to chemotherapy, the clients elected to proceed with a single fraction of palliative radiation therapy to the left side of the head (6-grey x 1 via manual set-up). He also received one dose of an MVPP protocol (mechlorethamine 3mg/m2 IV, vinblastine 2mg/m2 IV, procarbazine 50mg/m2 PO for 1 week, prednisolone 40 mg/m2 PO for 1 week) protocol. An update from the owner one week later reported improvement of the left sided facial swelling though the ventral edema was reportedly stable. However, eleven days after this treatment, he developed progressive edema along his limbs and ventrum. For the first time since diagnosis, he had trouble rising and was uncomfortable, and his owners elected to proceed with humane euthanasia, 63 days after initial presentation to CSU. A necropsy was not performed. \u0026nbsp;\u003c/p\u003e"},{"header":"DISCUSSION AND CONCLUSIONS","content":"\u003cp\u003eThis case report describes the clinical course of a dog with primary intramuscular lymphoma, a rarely reported form of lymphoma. Similar to prior case reports of this disease, the dog described here had an acute presentation of multifocal tumors. Presenting signs included limb swelling, edema, pain associated with the mass effects, and constitutional signs such as hyporexia and lethargy. In our case, cytology did elevate lymphoma as a differential early in the case work up, but histopathology was initially discordant with this diagnosis. Diagnosis typically relies on histopathology with IHC to confirm the diagnosis, and PARR may be utilized to further support a lymphoma diagnosis. \u0026nbsp;When treated, as evidenced in one previously published case report and in the dog described here, these masses can respond to chemotherapy however tend to progress rapidly even with aggressive therapy (5). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePreviously reported cases documented one presumed B-cell lymphoma and two cases with IHC confirmed T-cell lymphoma (4\u0026ndash;6). Interestingly, one case was reported to be CD3 and MUM-1 positive with a clonal T-cell population noted with PARR (6). While the case outlined in this report was negative for CD3 and CD20 with positive MUM-1 expression, the final diagnosis of T-cell Lymphoma with MUM-1 expression was made based on a clonal T-cell receptor population noted on PARR. This highlights the diagnostic challenge that can occur with round cell tumors, and that a multi-modal diagnostic approach utilizing multiple IHC markers and PARR is needed to obtain a definitive diagnosis, likely due to aberrant expression of markers not typically associated with these tumors. Advanced imaging also played a role in determining the extent of disease, particularly the use of contrast enhanced the masses, as they were not visible with non-contrast CT or ultrasound alone. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis case represents the longest response to treatment in a dog with primary intramuscular lymphoma at 63 days of overall survival time. To our knowledge, the only other case previously reported that was treated had a reported survival of 6 weeks (6). However, this patient was euthanized when progression occurred after first line therapy, and no rescue protocols were attempted while in our case the owners were willing to continue with further treatment as long as his quality of life was acceptable. This case highlights that this tumor type can respond to single-agent doxorubicin, Lomustine/L-SPAR, and MVPP protocols, though the response to each protocol was short-lived. Radiation therapy in this case reduced significant swelling rapidly, improving the dog\u0026rsquo;s quality of life, and may play a role in local disease control in other patients. Due to this dog\u0026rsquo;s rapid progression, monotherapy with DOX was pursued prior to the final diagnosis, and continued due to his response to this therapy. In retrospect knowing the final diagnosis, a CHOP-based protocol likely would have been our first line recommendation. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn conclusion, this case report summarizes the extensive diagnostic workup and treatment of a dog with primary intramuscular T-cell lymphoma. The limited literature to date highlights the rarity of this form of lymphoma in dogs. Literature in humans is also very scarce with only a handful of case reports with no consensus available for accurate diagnosis, treatment, and outcome data available. This case highlights that dogs with this diagnosis can respond to systemic chemotherapy and radiation therapy, though this response appears to be short-lived. Diagnosis in these cases can also be challenging, and it should be kept in mind that treatment may need to be pursued prior to final diagnosis. It may also be valuable to expedite cytology and biopsy with immunohistochemical and PARR analysis in suspect cases with multifocal intramuscular masses. Primary intramuscular lymphoma should be considered as a differential in patients with acute presentation of rapid progression of limb edema and multifocal masses. However, conclusions about treatment for these patients would ideally be reached with review of additional cases but given the rarity of this tumor type this will likely be challenging. \u0026nbsp;\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eL-SPAR: L-Asparaginase\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSQ: Subcutaneous\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDOX: doxorubicin \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIV: Intravenous\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIHC: immunohistochemistry \u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePARR: PCR for antigen receptor rearrangements \u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval and consent to participate: n/a \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eConsent for publication: The patient\u0026rsquo;s owner was contacted via email on 02DEC25 and provided permission for publication of the included information and photographs of the patient. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials: n/a \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompeting interests: The authors declare that they have no competing interests \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFunding: n/a \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; contributions: MG was the primary author with contributions from the remaining authors including editing and compilation of the figures included. PY provided interpretation of the CT and the included CT images. PS read the histopathology and guided IHC recommendations, and provided the included histopathology images. All authors read and approved the final manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAcknowledgements: The authors would like to thank this patient\u0026rsquo;s owners for providing permission for publication. They also provided routine updates on his status throughout his treatment, and several of the photos included here are from these updates, used with their permission. \u0026nbsp;\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAlexander V, Shenoy R, Korula A, Koshy M. Intramuscular lymphoma: uncommon presentation of Hodgkin\u0026rsquo;s disease. BMJ Case Rep. 2020 Aug;13(8):e229826. \u003c/li\u003e\n\u003cli\u003eGao S, Shu H, Yang H. Imaging features of skeletal muscle lymphoma: a case report and literature review. BMC Med Imaging. 2021 Dec;21(1):136. \u003c/li\u003e\n\u003cli\u003eChew FS, Schellingerhout D, Keel SB. Primary lymphoma of skeletal muscle. Am J Roentgenol. 1999 May;172(5):1370\u0026ndash;1370. \u003c/li\u003e\n\u003cli\u003eHarkin K, Kennedy G, Moore W, Schoning P. Skeletal muscle lymphoma in a bullmastiff. J Am Anim Hosp Assoc. 2000 Jan 1;36(1):63\u0026ndash;6. \u003c/li\u003e\n\u003cli\u003eThuilliez C, Watrelot-Virieux D, Chanut F, Fournel-Fleury C, Ponce F, Marchal T. Presumed Primary Muscular Lymphoma in a Dog. J Vet Diagn Invest. 2008 Nov;20(6):824\u0026ndash;6\u003c/li\u003e\n\u003cli\u003eLopes MG, Marchesi F, Haining H, Morris JS. Primary multifocal muscular T-cell lymphoma with cutaneous involvement in a dog: A case report and review of the literature. Vet Clin Pathol. 2021 Dec 1;50(4):584\u0026ndash;8. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"veterinary-oncology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Veterinary Oncology](https://veterinaryoncology.biomedcentral.com/)","snPcode":"44356","submissionUrl":"https://submission.springernature.com/new-submission/44356/3","title":"Veterinary Oncology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Intramuscular lymphoma, T-cell, MUM-1","lastPublishedDoi":"10.21203/rs.3.rs-8929002/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8929002/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e: In both humans and veterinary species, primary intramuscular lymphoma is a rarely reported condition. Limited literature available shows that these tumors are often multifocal, with clinical signs often including limb edema and swelling, and lameness. Signs are typically acute and rapidly progressive.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCase Presentation\u003c/strong\u003e: A 10-year-old castrated male dog with multifocal intramuscular masses was diagnosed as T-cell Lymphoma with aberrant MUM-1 expression. He presented due to rapidly progressive right hindlimb edema. The diagnosis was difficult to achieve in this case due to an unusual pattern of expression of surface markers. A combination of contrast CT, cytology, histopathology, immunohistochemistry, and PARR were necessary to achieve a final diagnosis. The dog had an initial rapid response to doxorubicin, but progressive disease was noted shortly after the third dose was administered. He was then treated with rescue chemotherapy protocols and focal radiation therapy. Despite these aggressive therapies, his disease was further progressive and due to poor quality of life humane euthanasia was pursued 63 days after initial presentation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e: Intramuscular lymphoma appears to be an aggressive subtype of lymphoma. Diagnosis can be difficult in these cases, and a multi-modal approach is often necessary. While these patients can respond well to chemotherapy and radiation therapy, the response is often short-lived, and prognosis remains guarded for these dogs.\u003c/p\u003e","manuscriptTitle":"Primary Intramuscular T-cell Lymphoma with MUM-1 Expression in a Dog","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-27 09:13:14","doi":"10.21203/rs.3.rs-8929002/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-12T11:22:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-08T16:39:45+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-05T16:50:57+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-05T11:31:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"241589726888316628231629996368536788914","date":"2026-02-25T12:54:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"317395703410675780785525490623374336547","date":"2026-02-24T16:45:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"290220156991205409548100826191898999420","date":"2026-02-24T12:29:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-23T20:58:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-23T08:28:16+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-23T08:23:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Veterinary Oncology","date":"2026-02-20T20:47:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"veterinary-oncology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Veterinary Oncology](https://veterinaryoncology.biomedcentral.com/)","snPcode":"44356","submissionUrl":"https://submission.springernature.com/new-submission/44356/3","title":"Veterinary Oncology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ce681dbe-24eb-4bfe-86df-b14d0fb07ddf","owner":[],"postedDate":"February 27th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-17T17:38:19+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-27 09:13:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8929002","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8929002","identity":"rs-8929002","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}