Question:medium
Which tumor is positive for TTF-1?
Which tumor is positive for TTF-1?
Show Hint
TTF-1 marks thyroid and lung type-II pneumocyte lineage — think which lung cancer forms glands and is the classic positive.
Updated On: Jun 22, 2026
- Sq (Squamous cell carcinoma)
- Small (Small cell carcinoma)
- Adeno Ca (Adenocarcinoma)
- Carcinoid
Show Solution
The Correct Option is C
Solution and Explanation
Marker-to-tissue reasoning.
Begin with what TTF-1 (NKX2-1) marks: cells of thyroid follicular and lung (alveolar type-II / Clara) lineage. So in a thoracic tumour, a TTF-1-positive result points to a tumour that recapitulates lung glandular epithelium.
Walk the four options through this filter:
• Squamous cell carcinoma - arises from bronchial squamous metaplasia, expresses $p40$ / $p63$ / $CK5/6$, and is TTF-1 NEGATIVE.
• Adenocarcinoma - derived from glandular/alveolar epithelium, the very lineage TTF-1 marks → TTF-1 POSITIVE. The image shows gland-forming tumour, matching this.
• Small cell carcinoma - neuroendocrine; often TTF-1 positive too, but the morphology and the classic single-best teaching answer point to adenocarcinoma.
• Carcinoid - low-grade neuroendocrine tumour, marked by chromogranin/synaptophysin, generally TTF-1 negative.
Resolution.
The tumour that is canonically and most usefully TTF-1 positive among these - and the one separating lung primary from squamous/metastatic mimics - is adenocarcinoma. ($answer = Option\ C$)
Takeaway: TTF-1 (+) + glandular morphology = lung adenocarcinoma; squamous and carcinoid are the TTF-1 (-) distractors.
Begin with what TTF-1 (NKX2-1) marks: cells of thyroid follicular and lung (alveolar type-II / Clara) lineage. So in a thoracic tumour, a TTF-1-positive result points to a tumour that recapitulates lung glandular epithelium.
Walk the four options through this filter:
• Squamous cell carcinoma - arises from bronchial squamous metaplasia, expresses $p40$ / $p63$ / $CK5/6$, and is TTF-1 NEGATIVE.
• Adenocarcinoma - derived from glandular/alveolar epithelium, the very lineage TTF-1 marks → TTF-1 POSITIVE. The image shows gland-forming tumour, matching this.
• Small cell carcinoma - neuroendocrine; often TTF-1 positive too, but the morphology and the classic single-best teaching answer point to adenocarcinoma.
• Carcinoid - low-grade neuroendocrine tumour, marked by chromogranin/synaptophysin, generally TTF-1 negative.
Resolution.
The tumour that is canonically and most usefully TTF-1 positive among these - and the one separating lung primary from squamous/metastatic mimics - is adenocarcinoma. ($answer = Option\ C$)
Takeaway: TTF-1 (+) + glandular morphology = lung adenocarcinoma; squamous and carcinoid are the TTF-1 (-) distractors.
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