A 60-year-old male smoker undergoes lobectomy for a peripheral lung mass. Histology shows malignant cells arranged in acini and glandular structures with mucin production; immunostaining is TTF-1 positive, CK7 positive, and CK20 negative. What is the diagnosis?
- A Squamous cell carcinoma of the lung
- B Small cell lung carcinoma
- C Pulmonary adenocarcinoma ✓
- D Large cell carcinoma
Explanation
The histological pattern (acinar/glandular with mucin), combined with TTF-1 positive and CK7 positive/CK20 negative immunoprofile, is characteristic of pulmonary adenocarcinoma — the most common lung cancer overall and the most frequent non-small-cell lung cancer in non-smokers and women. TTF-1 (thyroid transcription factor-1) is expressed in thyroid and lung epithelia. Squamous cell carcinoma is p40/p63 positive; small cell carcinoma is TTF-1 positive but also synaptophysin/chromogranin positive with small cell morphology; large cell carcinoma is a diagnosis of exclusion.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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