A 65-year-old ex-smoker presents with a peripheral lung mass arising from prior scar tissue. Microscopically it shows glandular structures producing mucin, positive for TTF-1 and CK7, negative for p40 and CK5/6. The diagnosis is:
- A Squamous cell carcinoma
- B Adenocarcinoma (scar carcinoma) ✓
- C Small cell carcinoma
- D Large cell carcinoma
Correct answer: B. Adenocarcinoma (scar carcinoma)
Explanation
This presentation describes a peripheral lung adenocarcinoma arising in a scar (scar carcinoma). The immunoprofile — TTF-1+, CK7+, p40−, CK5/6− — is characteristic of adenocarcinoma with pneumocytic/glandular differentiation. Squamous cell carcinoma is p40+/CK5/6+/TTF-1−; small cell carcinoma is TTF-1+ but also CD56+/synaptophysin+ with scant cytoplasm and salt-and-pepper chromatin; large cell carcinoma is negative for all lineage markers by definition.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.