Collision Tumor of Adenocarcinoma and Squamous Cell Carcinoma of the Gallbladder: a Rare Case Report with Histopathological and Immunohistochemical Insights

Collision Tumor of Adenocarcinoma and Squamous Cell Carcinoma of the Gallbladder: a Rare Case Report with Histopathological and Immunohistochemical Insights | 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 Collision Tumor of Adenocarcinoma and Squamous Cell Carcinoma of the Gallbladder: a Rare Case Report with Histopathological and Immunohistochemical Insights Niti Sureka, Shikhar Chohan, Sufian Zaheer This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9375584/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Background: Gallbladder carcinoma is the most common malignancy of the biliary tract, with adenocarcinoma being the predominant histological subtype. Collision tumors of the gallbladder, comprising two distinct malignant components without transitional morphology, are exceedingly rare and pose significant diagnostic and pathogenetic challenges. Case Presentation: We report a case of a 41-year-old female who presented with persistent right upper quadrant pain, weight loss, and imaging findings suggestive of a gallbladder mass with hepatic infiltration. The patient underwent open cholecystectomy with en bloc liver resection and regional lymphadenectomy. Gross examination revealed an exophytic mass in the gallbladder fundus infiltrating the liver bed. Histopathological evaluation demonstrated two distinct, non-intermingling malignant components- adenocarcinoma and squamous cell carcinoma—consistent with a collision tumor. The adenocarcinoma component showed infiltrative glands with mucin production, while the squamous component exhibited keratinization, intercellular bridges, and marked cytological atypia. Lymphovascular and perineural invasion were present. Immunohistochemistry demonstrated CK19 positivity in both glandular and squamous components, diffuse pan-cytokeratin (PanCK) expression in tumor cells, and strong nuclear p63 positivity in the squamous component. Conclusions: Collision tumors of the gallbladder are exceptionally rare and require careful histopathological evaluation to distinguish them from adenosquamous carcinoma. This case highlights the importance of recognizing distinct tumor components and underscores the aggressive biological behavior of such neoplasms. Gallbladder carcinoma Collision tumor Adenocarcinoma Squamous cell carcinoma Immunohistochemistry Figures Figure 1 Figure 2 Figure 3 Background Gallbladder carcinoma (GBC) is the most common malignancy of the biliary tract and demonstrates marked geographic variation, with the highest incidence reported in regions such as North India, East Asia, and South America [1,2]. Despite its relatively low global incidence, it is associated with a poor prognosis due to its aggressive nature and late clinical presentation [1]. Adenocarcinoma accounts for approximately 90–95% of all gallbladder malignancies and represents the most extensively studied histological subtype [3]. In contrast, less common variants such as adenosquamous carcinoma (ASC) and pure squamous cell carcinoma comprise a small proportion of cases but are associated with more aggressive behavior, including rapid growth and a higher propensity for local invasion into adjacent organs [4,5]. Collision tumors are defined as the coexistence of two histologically distinct malignant neoplasms occurring in the same anatomical site without intermingling or transitional morphology [6]. Such tumors are exceedingly rare in the gallbladder, with only a limited number of cases reported in the literature [7]. Distinguishing collision tumors from adenosquamous carcinoma is critical, as ASC demonstrates a mixed or transitional pattern between glandular and squamous components, whereas collision tumors show sharply demarcated, independent tumor populations, suggesting a different pathogenesis [4,6]. Given the rarity and diagnostic challenges associated with these tumors, we report a case of a collision tumor of the gallbladder comprising distinct adenocarcinoma and squamous cell carcinoma components, with emphasis on its clinicopathological and immunohistochemical features. Case presentation A 41-year-old female presented with a six-month history of dull, persistent right upper quadrant pain associated with nausea, vomiting, and significant weight loss. There was no history of jaundice, fever, or altered bowel habits. Her past medical and surgical history was unremarkable, and there was no family history of malignancy. On examination, she had tenderness in the right hypochondrium without a palpable mass. Laboratory investigations revealed mildly elevated alkaline phosphatase and CA 19-9 levels, while liver function tests and hematological parameters were within normal limits. Radiological evaluation included ultrasonography, which demonstrated a distended gallbladder with focal convex wall thickening at the fundus measuring 3.5 × 1.7 cm, along with multiple calculi (6–8 mm) in the neck region and associated sludge. No definite infiltration into the adjacent liver parenchyma was noted on ultrasound. Contrast-enhanced computed tomography (CECT) revealed a heterogeneously enhancing mass involving the anterior fundal wall of the gallbladder, measuring 4.3 × 2.3 cm with a maximum thickness of 22 mm. There was loss of fat planes with the adjacent liver and evidence of direct hepatic infiltration [Figure 1]. Multiple necrotic, rim-enhancing periportal lymph nodes were identified, the largest measuring 2.8 × 2.2 cm, along with a necrotic right gastric lymph node. These findings were suggestive of nodal metastasis. The preoperative stage was assessed as T3N2M0. The patient underwent extended cholecystectomy with non-anatomical wedge resection of adjacent liver and lymph node sampling under general anesthesia. Intraoperatively, the gallbladder was distended with pus (pyocele) and multiple calculi. An exophytic growth was identified in the fundus, infiltrating the adjacent liver. Calot’s triangle was found to be frozen. Enlarged periportal and right gastric lymph nodes were noted. No gross peritoneal or omental metastases were identified; however, a suspicious lesion was observed in the left lobe of the liver, and a biopsy was obtained. Gross examination revealed an irregular, friable, gray-white tumor measuring 5.5 × 4 × 3 cm in the fundus, infiltrating the liver bed, with areas of necrosis[Figure 1]. Multiple gallstones were also present. Histopathological examination confirmed a biphasic malignant neoplasm consistent with adenosquamous carcinoma, composed of both glandular and predominant (>80%) squamous components[Figure 2]. The adenocarcinoma component formed irregular, infiltrative glands with mucin production, invading beyond the muscular layer. The squamous component showed sheets of polygonal cells with abundant eosinophilic cytoplasm, keratin pearl formation, intercellular bridges, marked nuclear atypia, and frequent mitoses, including atypical forms. Lymphovascular and perineural invasion were present. Tumor infiltration into the adjacent liver parenchyma was noted. Metastatic deposits were identified in the sampled lymph nodes and in the biopsy from the left lobe of the liver, confirming postoperative staging of T3N2M1. Immunohistochemistry demonstrated CK19 positivity in both components, diffuse pan-cytokeratin expression, and strong nuclear p63 positivity in the squamous component[Figure 3]. Discussion and Conclusion Adenocarcinoma is the predominant histological subtype of gallbladder carcinoma (GBC), while squamous and adenosquamous variants are uncommon, accounting for a small proportion of cases [1,3]. These variants are associated with more aggressive clinical behavior, often presenting at advanced stages with rapid local invasion into adjacent organs, particularly the liver [4,5,8]. Collision tumors of the gallbladder are exceedingly rare and are defined by the coexistence of two histologically distinct malignant components arising in the same anatomical location without intermingling or transitional morphology [6,9]. In contrast, adenosquamous carcinoma demonstrates a gradual transition between glandular and squamous elements, supporting a monoclonal origin with divergent differentiation [4,6]. The absence of a transitional zone in our case, along with the presence of two sharply demarcated components, strongly supports the diagnosis of a collision tumor. The histogenesis of collision tumors remains uncertain. Several hypotheses have been proposed, including the independent synchronous development of two neoplasms, divergence from a common pluripotent stem cell, or the influence of a shared carcinogenic microenvironment such as chronic inflammation [5,7,9]. In the gallbladder, long-standing cholelithiasis and chronic cholecystitis are well-recognized risk factors and may play a role in the development of such rare composite neoplasms [2,5,10]. Clinically and radiologically, collision tumors are indistinguishable from conventional gallbladder carcinoma, typically presenting with nonspecific symptoms such as right upper quadrant pain, nausea, and weight loss [2,10]. Imaging often reveals a mass lesion with features of local invasion, as observed in our case, which demonstrated hepatic infiltration. Histopathological examination remains the gold standard for diagnosis. In the present case, the adenocarcinoma component showed infiltrative glandular architecture with mucin production, while the squamous component exhibited keratinization, intercellular bridges, and marked cytological atypia. Immunohistochemistry further confirmed the biphasic nature of the tumor, with CK7 and CEA positivity in the glandular component and p63 and CK5/6 positivity in the squamous component, consistent with prior reports [4,5,11]. The predominance of the squamous component has been associated with higher proliferative activity and more aggressive tumor behavior, which may explain the high Ki-67 index and early local invasion observed in this case [5,8]. Histopathological evaluation confirmed metastatic involvement of lymph nodes and liver. Surgical resection remains the mainstay of treatment for gallbladder malignancies. However, due to the aggressive nature of these tumors and their tendency for late presentation, overall prognosis remains poor [2,4,10]. In conclusion, collision tumors of the gallbladder are exceptionally rare and pose significant diagnostic challenges. Careful histopathological evaluation is essential to distinguish them from adenosquamous carcinoma. Recognition of this entity is important for accurate classification and may provide insights into tumor biology and pathogenesis. Declarations Financial disclosure statement : There is no financial support. Source(s) of support/ funding: Nil Ethical Approval - This report was conducted in accordance with the principles of the Declaration of Helsinki. Consent for Publication - Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the signed consent is available for review by the Editor-in-Chief upon request. Consent to Participate - Written informed consent was obtained from the patient for participation in this case report. AI Declaration During the preparation of this manuscript the author(s) used Chatgpt in order to check language. After using this tool, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication. Conflict of Interest - The authors declare that they have no competing interests. Author Contribution Conceptualisation: SZ, NS, SC Writing original draft: SZ, NS, SC Writing-Review and editing: SZ, SC Supervision: SZ This paper has been prepared by the abovementioned authors and agreed upon for submission. The manuscript is an original work and has not been submitted elsewhere for publication. Availability of data and material – Yes References Bray F, Ferlay J, Soerjomataram I, Siegel RL, Torre LA, Jemal A. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide. CA Cancer J Clin. 2018;68(6):394–424. Hundal R, Shaffer EA. Gallbladder cancer: epidemiology and outcome. Clin Epidemiol. 2014;6:99–109. WHO Classification of Tumours Editorial Board. Digestive System Tumours. 5th ed. Lyon: IARC; 2019. Roa JC, Tapia O, Cakir A, et al. Squamous cell and adenosquamous carcinomas of the gallbladder: clinicopathological analysis. Mod Pathol. 2011;24(8):1069–78. Gulwani HV, Gupta S, Kaur S. Squamous cell and adenosquamous carcinoma of gallbladder: clinicopathological study. Indian J Surg Oncol. 2017;8(4):560–6. Meyer R. Beitrag zur Verständigung über die Namengebung in der Geschwulstlehre. Zentralbl Allg Pathol. 1919;30:291–6. Niu X, Zhao J, Wang L, et al. Clinicopathological characteristics and outcomes of rare histologic subtypes of gallbladder cancer. PLoS ONE. 2018;13(6):e0198809. Zhang X et al. Clinicopathological features of adenosquamous carcinoma of the gallbladder. Oncol Lett. 2020. Spagnolo DV, Heenan PJ. Collision carcinoma: concept and implications. Histopathology. 1980;4:173–82. Karampa AD, Gkizas G, Kyrochristou G, et al. Adenosquamous carcinoma of gallbladder. Cureus. 2025;17:e77811. Davis T, Moudy P, Abdelgawad M, et al. Gallbladder adenosquamous carcinoma: case report and review. J Surg Case Rep. 2021;2021:rjab365. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 29 Apr, 2026 Reviewers agreed at journal 29 Apr, 2026 Reviewers agreed at journal 25 Apr, 2026 Reviews received at journal 23 Apr, 2026 Reviewers agreed at journal 23 Apr, 2026 Reviewers invited by journal 23 Apr, 2026 Editor assigned by journal 15 Apr, 2026 Submission checks completed at journal 15 Apr, 2026 First submitted to journal 10 Apr, 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-9375584","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":633610209,"identity":"2566559f-daea-4591-a946-29ee95cc61e5","order_by":0,"name":"Niti Sureka","email":"","orcid":"","institution":"Vardhman Mahavir Medical College \u0026 Safdarjung Hospital","correspondingAuthor":false,"prefix":"","firstName":"Niti","middleName":"","lastName":"Sureka","suffix":""},{"id":633610210,"identity":"c985ce39-db6b-4146-b766-018bb1f707d4","order_by":1,"name":"Shikhar Chohan","email":"","orcid":"","institution":"Vardhman Mahavir Medical College \u0026 Safdarjung Hospital","correspondingAuthor":false,"prefix":"","firstName":"Shikhar","middleName":"","lastName":"Chohan","suffix":""},{"id":633610211,"identity":"15e5228d-ff61-44ed-8543-26d10e08ea92","order_by":2,"name":"Sufian Zaheer","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIiWNgGAWjYFACxgcHQJQBiPgAxGzsBLUwG8C1MM4AaWEmQgsDTAszD1iAgAb5GcmMB37uqJM3Z28+9tnm1zZ5PmYGxg8fc3BrMbiRzHCw9wyb4c6eY8mzc/tuG7YxMzBLztyGR4tE/oEDvG08jBtu5Bgz5/bcZgRqYWPmxaMF6DCGg3/bJOw33H//mdmy57Y9QS0MQIcd5m0zSNxwg4eZmeHH7USCWgzOPGY4LNuWkLzhTJoxY2/D7eQ2ZsZmvH6Rb09m/vi2rc52w/HDjxl+/LltO7+9+eCHj/gchgIY28BkA7HqQeAPKYpHwSgYBaNgpAAAWn1R2gciW2kAAAAASUVORK5CYII=","orcid":"","institution":"Vardhman Mahavir Medical College \u0026 Safdarjung Hospital","correspondingAuthor":true,"prefix":"","firstName":"Sufian","middleName":"","lastName":"Zaheer","suffix":""}],"badges":[],"createdAt":"2026-04-10 06:53:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9375584/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9375584/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109037941,"identity":"74571ac8-b951-4a22-bd79-1e188ea8d4d9","added_by":"auto","created_at":"2026-05-12 03:00:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2661671,"visible":true,"origin":"","legend":"\u003cp\u003eRadiological and gross findings of gallbladdercollision tumor of the gallbladder.\u003cbr\u003e\n(A) Axial contrast-enhanced CT image showing a heterogeneously enhancing mass lesion (arrows) arising from the gallbladder fundus with loss of fat planes and infiltration into adjacent liver parenchyma. (B) Coronal CT section demonstrating the gallbladder mass with hepatic extension. (C–D) Gross specimen showing an irregular, exophytic gray-white tumor in the fundus with areas of necrosis and friability. (E) Posterior aspect of the specimen (liver bed surface) showing tumor infiltration into the hepatic bed.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-9375584/v1/3a39c4063ae6627281df27d0.png"},{"id":109068286,"identity":"0c9bc858-f501-4571-9bdb-aae48b2180b8","added_by":"auto","created_at":"2026-05-12 10:05:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":4966367,"visible":true,"origin":"","legend":"\u003cp\u003eHistopathological features of collision tumor of the gallbladder (H\u0026amp;E). (A) Low-power view showing a biphasic tumor with adenocarcinoma (A) and squamous (S) components. (B–C) Adenocarcinoma component demonstrating infiltrative glands with mucin production and cytologic atypia. (D–E) Squamous component showing keratin pearl formation, intercellular bridges, and marked nuclear pleomorphism.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-9375584/v1/d55d7f8a3fce0a38615d6c54.png"},{"id":109037943,"identity":"6713c8b2-707b-43b7-920d-e916121e56d2","added_by":"auto","created_at":"2026-05-12 03:00:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4588180,"visible":true,"origin":"","legend":"\u003cp\u003eImmunohistochemical profile of the tumor. (A) CK19 highlighting both squamous and the glandular (adenocarcinoma) component. (B) Pan-cytokeratin (PanCK) showing diffuse epithelial positivity in tumor cells of both the components.\u003cbr\u003e\n(C) p63 demonstrating strong nuclear positivity in the squamous component, confirming squamous differentiation.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-9375584/v1/69cd1dbc36a1d69d2d3813f6.png"},{"id":109204721,"identity":"09d679a9-908e-4dc0-8659-75a5c0493462","added_by":"auto","created_at":"2026-05-13 15:01:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":11735594,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9375584/v1/950ecd04-e359-474c-8519-7595e22c1306.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Collision Tumor of Adenocarcinoma and Squamous Cell Carcinoma of the Gallbladder: a Rare Case Report with Histopathological and Immunohistochemical Insights","fulltext":[{"header":"Background","content":"\u003cp\u003eGallbladder carcinoma (GBC) is the most common malignancy of the biliary tract and demonstrates marked geographic variation, with the highest incidence reported in regions such as North India, East Asia, and South America [1,2]. Despite its relatively low global incidence, it is associated with a poor prognosis due to its aggressive nature and late clinical presentation [1].\u003c/p\u003e\n\u003cp\u003eAdenocarcinoma accounts for approximately 90\u0026ndash;95% of all gallbladder malignancies and represents the most extensively studied histological subtype [3]. In contrast, less common variants such as adenosquamous carcinoma (ASC) and pure squamous cell carcinoma comprise a small proportion of cases but are associated with more aggressive behavior, including rapid growth and a higher propensity for local invasion into adjacent organs [4,5].\u003c/p\u003e\n\u003cp\u003eCollision tumors are defined as the coexistence of two histologically distinct malignant neoplasms occurring in the same anatomical site without intermingling or transitional morphology [6]. Such tumors are exceedingly rare in the gallbladder, with only a limited number of cases reported in the literature [7].\u003c/p\u003e\n\u003cp\u003eDistinguishing collision tumors from adenosquamous carcinoma is critical, as ASC demonstrates a mixed or transitional pattern between glandular and squamous components, whereas collision tumors show sharply demarcated, independent tumor populations, suggesting a different pathogenesis [4,6].\u003c/p\u003e\n\u003cp\u003eGiven the rarity and diagnostic challenges associated with these tumors, we report a case of a collision tumor of the gallbladder comprising distinct adenocarcinoma and squamous cell carcinoma components, with emphasis on its clinicopathological and immunohistochemical features.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eA 41-year-old female presented with a six-month history of dull, persistent right upper quadrant pain associated with nausea, vomiting, and significant weight loss. There was no history of jaundice, fever, or altered bowel habits. Her past medical and surgical history was unremarkable, and there was no family history of malignancy.\u003c/p\u003e\n\u003cp\u003eOn examination, she had tenderness in the right hypochondrium without a palpable mass. Laboratory investigations revealed mildly elevated alkaline phosphatase and CA 19-9 levels, while liver function tests and hematological parameters were within normal limits.\u003c/p\u003e\n\u003cp\u003eRadiological evaluation included ultrasonography, which demonstrated a distended gallbladder with focal convex wall thickening at the fundus measuring 3.5 \u0026times; 1.7 cm, along with multiple calculi (6\u0026ndash;8 mm) in the neck region and associated sludge. No definite infiltration into the adjacent liver parenchyma was noted on ultrasound.\u003c/p\u003e\n\u003cp\u003eContrast-enhanced computed tomography (CECT) revealed a heterogeneously enhancing mass involving the anterior fundal wall of the gallbladder, measuring 4.3 \u0026times; 2.3 cm with a maximum thickness of 22 mm. There was loss of fat planes with the adjacent liver and evidence of direct hepatic infiltration [Figure 1]. Multiple necrotic, rim-enhancing periportal lymph nodes were identified, the largest measuring 2.8 \u0026times; 2.2 cm, along with a necrotic right gastric lymph node. These findings were suggestive of nodal metastasis. The preoperative stage was assessed as T3N2M0.\u003c/p\u003e\n\u003cp\u003eThe patient underwent extended cholecystectomy with non-anatomical wedge resection of adjacent liver and lymph node sampling under general anesthesia. Intraoperatively, the gallbladder was distended with pus (pyocele) and multiple calculi. An exophytic growth was identified in the fundus, infiltrating the adjacent liver. Calot\u0026rsquo;s triangle was found to be frozen. Enlarged periportal and right gastric lymph nodes were noted. No gross peritoneal or omental metastases were identified; however, a suspicious lesion was observed in the left lobe of the liver, and a biopsy was obtained.\u003c/p\u003e\n\u003cp\u003eGross examination revealed an irregular, friable, gray-white tumor measuring 5.5 \u0026times; 4 \u0026times; 3 cm in the fundus, infiltrating the liver bed, with areas of necrosis[Figure 1]. Multiple gallstones were also present. Histopathological examination confirmed a biphasic malignant neoplasm consistent with adenosquamous carcinoma, composed of both glandular and predominant (\u0026gt;80%) squamous components[Figure 2]. The adenocarcinoma component formed irregular, infiltrative glands with mucin production, invading beyond the muscular layer. The squamous component showed sheets of polygonal cells with abundant eosinophilic cytoplasm, keratin pearl formation, intercellular bridges, marked nuclear atypia, and frequent mitoses, including atypical forms. Lymphovascular and perineural invasion were present. Tumor infiltration into the adjacent liver parenchyma was noted. Metastatic deposits were identified in the sampled lymph nodes and in the biopsy from the left lobe of the liver, confirming postoperative staging of T3N2M1.\u003c/p\u003e\n\u003cp\u003eImmunohistochemistry demonstrated CK19 positivity in both components, diffuse pan-cytokeratin expression, and strong nuclear p63 positivity in the squamous component[Figure 3].\u003c/p\u003e"},{"header":"Discussion and Conclusion","content":"\u003cp\u003eAdenocarcinoma is the predominant histological subtype of gallbladder carcinoma (GBC), while squamous and adenosquamous variants are uncommon, accounting for a small proportion of cases [1,3]. These variants are associated with more aggressive clinical behavior, often presenting at advanced stages with rapid local invasion into adjacent organs, particularly the liver [4,5,8].\u003c/p\u003e\n\u003cp\u003eCollision tumors of the gallbladder are exceedingly rare and are defined by the coexistence of two histologically distinct malignant components arising in the same anatomical location without intermingling or transitional morphology [6,9]. In contrast, adenosquamous carcinoma demonstrates a gradual transition between glandular and squamous elements, supporting a monoclonal origin with divergent differentiation [4,6]. The absence of a transitional zone in our case, along with the presence of two sharply demarcated components, strongly supports the diagnosis of a collision tumor.\u003c/p\u003e\n\u003cp\u003eThe histogenesis of collision tumors remains uncertain. Several hypotheses have been proposed, including the independent synchronous development of two neoplasms, divergence from a common pluripotent stem cell, or the influence of a shared carcinogenic microenvironment such as chronic inflammation [5,7,9]. In the gallbladder, long-standing cholelithiasis and chronic cholecystitis are well-recognized risk factors and may play a role in the development of such rare composite neoplasms [2,5,10].\u003c/p\u003e\n\u003cp\u003eClinically and radiologically, collision tumors are indistinguishable from conventional gallbladder carcinoma, typically presenting with nonspecific symptoms such as right upper quadrant pain, nausea, and weight loss [2,10]. Imaging often reveals a mass lesion with features of local invasion, as observed in our case, which demonstrated hepatic infiltration.\u003c/p\u003e\n\u003cp\u003eHistopathological examination remains the gold standard for diagnosis. In the present case, the adenocarcinoma component showed infiltrative glandular architecture with mucin production, while the squamous component exhibited keratinization, intercellular bridges, and marked cytological atypia. Immunohistochemistry further confirmed the biphasic nature of the tumor, with CK7 and CEA positivity in the glandular component and p63 and CK5/6 positivity in the squamous component, consistent with prior reports [4,5,11].\u003c/p\u003e\n\u003cp\u003eThe predominance of the squamous component has been associated with higher proliferative activity and more aggressive tumor behavior, which may explain the high Ki-67 index and early local invasion observed in this case [5,8]. Histopathological evaluation confirmed metastatic involvement of lymph nodes and liver. Surgical resection remains the mainstay of treatment for gallbladder malignancies. However, due to the aggressive nature of these tumors and their tendency for late presentation, overall prognosis remains poor [2,4,10].\u003c/p\u003e\n\u003cp\u003eIn conclusion, collision tumors of the gallbladder are exceptionally rare and pose significant diagnostic challenges. Careful histopathological evaluation is essential to distinguish them from adenosquamous carcinoma. Recognition of this entity is important for accurate classification and may provide insights into tumor biology and pathogenesis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFinancial disclosure statement\u003c/strong\u003e: There is no financial support.\u003c/p\u003e\n\u003cp\u003eSource(s) of support/ funding: Nil\u003c/p\u003e\u003cp\u003e \u003ch2\u003eEthical Approval -\u003c/h2\u003e \u003cp\u003eThis report was conducted in accordance with the principles of the Declaration of Helsinki.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for Publication -\u003c/strong\u003e \u003cp\u003e Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the signed consent is available for review by the Editor-in-Chief upon request.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent to Participate -\u003c/strong\u003e \u003cp\u003e Written informed consent was obtained from the patient for participation in this case report.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eAI Declaration\u003c/h2\u003e \u003cp\u003eDuring the preparation of this manuscript the author(s) used Chatgpt in order to check language. After using this tool, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConflict of Interest -\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualisation: SZ, NS, SC Writing original draft: SZ, NS, SC Writing-Review and editing: SZ, SC Supervision: SZ This paper has been prepared by the abovementioned authors and agreed upon for submission. The manuscript is an original work and has not been submitted elsewhere for publication.\u003c/p\u003e\u003ch2\u003eAvailability of data and material \u0026ndash;\u003c/h2\u003e \u003cp\u003eYes\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cspan\u003eBray F, Ferlay J, Soerjomataram I, Siegel RL, Torre LA, Jemal A. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide. CA Cancer J Clin. 2018;68(6):394\u0026ndash;424.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eHundal R, Shaffer EA. Gallbladder cancer: epidemiology and outcome. Clin Epidemiol. 2014;6:99\u0026ndash;109.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eWHO Classification of Tumours Editorial Board. Digestive System Tumours. 5th ed. Lyon: IARC; 2019.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRoa JC, Tapia O, Cakir A, et al. Squamous cell and adenosquamous carcinomas of the gallbladder: clinicopathological analysis. Mod Pathol. 2011;24(8):1069\u0026ndash;78.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eGulwani HV, Gupta S, Kaur S. Squamous cell and adenosquamous carcinoma of gallbladder: clinicopathological study. Indian J Surg Oncol. 2017;8(4):560\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMeyer R. Beitrag zur Verst\u0026auml;ndigung \u0026uuml;ber die Namengebung in der Geschwulstlehre. Zentralbl Allg Pathol. 1919;30:291\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eNiu X, Zhao J, Wang L, et al. Clinicopathological characteristics and outcomes of rare histologic subtypes of gallbladder cancer. PLoS ONE. 2018;13(6):e0198809.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eZhang X et al. Clinicopathological features of adenosquamous carcinoma of the gallbladder. Oncol Lett. 2020.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSpagnolo DV, Heenan PJ. Collision carcinoma: concept and implications. Histopathology. 1980;4:173\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eKarampa AD, Gkizas G, Kyrochristou G, et al. Adenosquamous carcinoma of gallbladder. Cureus. 2025;17:e77811.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eDavis T, Moudy P, Abdelgawad M, et al. Gallbladder adenosquamous carcinoma: case report and review. J Surg Case Rep. 2021;2021:rjab365.\u003c/span\u003e\u003cspan\u003e\u003c/span\u003e\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":false,"email":"[email protected]","identity":"surgical-and-experimental-pathology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"saep","sideBox":"Learn more about [Surgical and Experimental Pathology](http://surgexppathol.biomedcentral.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/SAEP/default.aspx","title":"Surgical and Experimental Pathology","twitterHandle":"@OncoBioMed","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Gallbladder carcinoma, Collision tumor, Adenocarcinoma, Squamous cell carcinoma, Immunohistochemistry","lastPublishedDoi":"10.21203/rs.3.rs-9375584/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9375584/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eGallbladder carcinoma is the most common malignancy of the biliary tract, with adenocarcinoma being the predominant histological subtype. Collision tumors of the gallbladder, comprising two distinct malignant components without transitional morphology, are exceedingly rare and pose significant diagnostic and pathogenetic challenges.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCase Presentation:\u003c/strong\u003e We report a case of a 41-year-old female who presented with persistent right upper quadrant pain, weight loss, and imaging findings suggestive of a gallbladder mass with hepatic infiltration. The patient underwent open cholecystectomy with en bloc liver resection and regional lymphadenectomy. Gross examination revealed an exophytic mass in the gallbladder fundus infiltrating the liver bed. Histopathological evaluation demonstrated two distinct, non-intermingling malignant components- adenocarcinoma and squamous cell carcinoma—consistent with a collision tumor. The adenocarcinoma component showed infiltrative glands with mucin production, while the squamous component exhibited keratinization, intercellular bridges, and marked cytological atypia. Lymphovascular and perineural invasion were present. Immunohistochemistry demonstrated CK19 positivity in both glandular and squamous components, diffuse pan-cytokeratin (PanCK) expression in tumor cells, and strong nuclear p63 positivity in the squamous component.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions:\u003c/strong\u003eCollision tumors of the gallbladder are exceptionally rare and require careful histopathological evaluation to distinguish them from adenosquamous carcinoma. This case highlights the importance of recognizing distinct tumor components and underscores the aggressive biological behavior of such neoplasms.\u003c/p\u003e","manuscriptTitle":"Collision Tumor of Adenocarcinoma and Squamous Cell Carcinoma of the Gallbladder: a Rare Case Report with Histopathological and Immunohistochemical Insights","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-12 03:00:51","doi":"10.21203/rs.3.rs-9375584/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-29T09:30:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"146132379447492640578157887399278260025","date":"2026-04-29T09:26:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"23667378090903765364384575990629483545","date":"2026-04-25T23:48:30+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-23T13:19:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"174432943464417575710308809176982276395","date":"2026-04-23T12:53:11+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-23T12:31:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-15T06:54:43+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-15T06:54:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Surgical and Experimental Pathology","date":"2026-04-10T06:43:25+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":false,"email":"[email protected]","identity":"surgical-and-experimental-pathology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"saep","sideBox":"Learn more about [Surgical and Experimental Pathology](http://surgexppathol.biomedcentral.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/SAEP/default.aspx","title":"Surgical and Experimental Pathology","twitterHandle":"@OncoBioMed","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0f52947a-b68d-407f-9145-3077bffbdf5f","owner":[],"postedDate":"May 12th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-12T03:00:51+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-12 03:00:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9375584","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9375584","identity":"rs-9375584","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}