Case Reports Open access

Gastric/pancreatobiliary-type differentiation in colorectal adenocarcinoma: a rare and aggressive case in a young adult

Authors

Published
16 September 2026
Section
Case Reports
DOI
10.4081/crest.2026.52

Abstract

Colorectal cancer (CRC) is a leading cause of cancer-related morbidity and mortality worldwide. Although most CRCs exhibit a characteristic immunohistochemical profile, rare variants with unusual differentiation patterns can pose significant diagnostic challenges and carry an adverse prognosis. We report a case of an aggressive colorectal adenocarcinoma with gastric/pancreatobiliary-type differentiation in a young adult. A 29-year-old woman presented with a 2-year history of melena, constipation, fatigue, and weight loss. Imaging and colonoscopy revealed a circumferential stenosing sigmoid colon mass with suspected peritoneal involvement. Histopathological examination demonstrated a moderately to poorly differentiated adenocarcinoma. Immunohistochemistry showed an atypical profile for colorectal origin, with positivity for CK7, MUC1, and MUC5AC, and negativity for CK20, CDX2, SATB2, and MUC2. Mismatch repair proteins were intact, indicating microsatellite stability. Surgical exploration revealed locally advanced disease with direct invasion of adjacent small bowel, appendix, and abdominal wall. En bloc resection was performed, and final pathology confirmed pT4bN2b disease with lymphovascular invasion and extranodal extension. This case highlights a rare immunophenotypic subtype of colorectal adenocarcinoma that mimics gastric or pancreatobiliary differentiation. Recognition of this entity is essential to avoid misclassification as metastatic disease from an extraintestinal primary and to ensure accurate staging and management. Awareness of such aggressive variants is particularly important given their association with poor prognostic features despite young patient age.

Keywords

Ethics Approval

No ethical committee approval was required for this case report by the Department because this article does not contain any studies with human participants or animals. Informed consent was obtained from the patient included in this study.

Data Availability Statement

All data underlying the findings are fully available.

References

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