A tumor biopsy immunohistochemistry panel shows diffuse strong CK7 positivity, CK20 negativity, TTF-1 positivity, and napsin A positivity. This immunoprofile is most consistent with:
- A Lung adenocarcinoma ✓
- B Merkel cell carcinoma
- C Colorectal adenocarcinoma
- D Hepatocellular carcinoma
Correct answer: A. Lung adenocarcinoma
Explanation
Lung adenocarcinoma is CK7+, CK20−, TTF-1+, napsin A+; this combination is highly specific for pulmonary origin. Colorectal carcinoma is CK7−/CK20+. Merkel cell carcinoma is CK20+ with a dot-like pattern and neuroendocrine markers; TTF-1 is negative. HCC is typically CK7−/CK20−, AFP+, Hep Par-1+. TTF-1 and napsin A together are the most reliable IHC markers to identify lung adenocarcinoma in an unknown primary workup.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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