A 60-year-old male smoker has a peripheral lung mass with pleural puckering. Biopsy shows glandular architecture with mucin production and TTF-1 positive staining. EGFR mutation testing is positive. The MOST likely diagnosis is:
- A Squamous cell carcinoma
- B Adenocarcinoma ✓
- C Small cell carcinoma
- D Large cell carcinoma
Correct answer: B. Adenocarcinoma
Explanation
Pulmonary adenocarcinoma is the most common lung cancer overall and the most common in non-smokers and women. It typically arises peripherally, shows glandular/acinar architecture, produces mucin, and is TTF-1 and Napsin-A positive. EGFR activating mutations (exons 19/21) occur predominantly in adenocarcinoma and predict response to EGFR tyrosine kinase inhibitors. Squamous cell carcinoma is centrally located, p40/CK5/6 positive, and not usually EGFR mutated.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.