A 55-year-old woman has bilateral solid ovarian masses. Histology reveals signet-ring cells with abundant extracellular mucin. Immunohistochemistry shows CK20 and CDX2 positive, CK7 negative. Where is the most likely primary site?
- A Ovary
- B Colorectum ✓
- C Appendix
- D Breast
Correct answer: B. Colorectum
Explanation
This is a Krukenberg tumor from a colorectal primary. CK20 positive, CK7 negative, and CDX2 positive immunoprofile strongly favors colorectal origin over appendiceal (which is often CK7 positive) or primary ovarian mucinous tumors (CK7 positive, CK20 negative). Bilateral signet-ring cell morphology in the ovary is metastatic until proven otherwise.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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