CUP — SCE Medical Oncology MCQ

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ModerateCancer of Unknown PrimaryCUPSCE Medical Oncology

A 50-year-old woman presents with peritoneal carcinomatosis. Biopsy shows poorly differentiated adenocarcinoma. IHC: CK7+, CK20+, CDX2+, PAX8-. CT shows no definite colonic or appendiceal primary. What is the most likely primary site based on the immunoprofile?

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Correct answer: C — Colorectal/appendiceal

CK7+/CK20+/CDX2+ immunoprofile in peritoneal adenocarcinoma strongly suggests colorectal or appendiceal origin. CDX2 is a highly specific intestinal marker. Even without an identifiable luminal primary, this immunoprofile should prompt colonoscopy and appendiceal assessment. CK7+/CK20+ can be seen in appendiceal, pancreaticobiliary and some colorectal primaries. The presence of CDX2 tips the balance toward colorectal/appendiceal. Treatment should follow colorectal cancer protocols.

Reference: NICE NG36 Cancer of unknown primary; ESMO 2024 CUP Guidelines