Ultrastructural and immunocytochemical definition of component neoplasms in an unusual gastro-oesophageal collision tumour.

An unusual collision tumour (concrescence of two neighbouring independent neoplasms) is reported. One tumour was a small cell undifferentiated (oat cell) carcinoma of the lower oesophagus and the other was a gastro-oesophageal adenocarcinoma. There was little intermingling of the two patterns. The adenocarcinoma stained strongly positive for mucin and carcinoembryonic antigen (CEA), but the small cell carcinoma was negative for both and also argyrophil-negative; both were negative for neurone-specific enolase and common leukocyte antigen. Ultrastructural study showed extra-cellular glandular lumina lined by cells with apical microvilli and junctional complexes in the adenocarcinoma; primitive cells without tonofilaments or dense-core granules, and joined by rudimentary desmosomes were seen in the small cell carcinoma. Collision carcinomas may result from a carcinogenic stimulus affecting two neighbouring regions of mucosa or may simply be the chance apposition of two unrelated tumours.