Pulmonary adenocarcinoma is a common neoplasm, yet the one with enteric or intestinal differentiation poses a diagnostic challenge to pathologists as it shares a common immunohistochemical profile with metastatic colorectal carcinoma. We report a case of a 61-year-old woman. She was on surveillance when incidentally she was discovered to have multiple bilateral lung nodules on imaging; the largest was surgically removed for histological examination. Morphology was consistent with a moderately differentiated adenocarcinoma .The tumour cells were positive for cytokeratin (CK) 7, CDX2, CK20 and were negative for thyroid transcription factor 1. The morphology and immune histochemical profile raised the differential diagnosis of a metastatic colorectal carcinoma and a primary lung adenocarcinoma with enteric differentiation. On the basis of morphology and CK7 positivity we established the diagnosis of enteric-type adenocarcinoma of primary lung origin. She has completed planned courses of palliative chemotherapy and remains on surveillance.
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