Case report: esophageal collision tumor (oat cell carcinoma and adenocarcinoma) in Barrett's esophagus: immunohistochemical, electron microscopy and LOH analysis.

We report a case of an esophageal collision tumor composed of adenocarcinoma and oat cell carcinoma. Both tumors appeared to arise from dysplastic Barrett's mucosae in a 75-year-old man. Immunohistochemical stains and electron microscopy demonstrated a separate identity for each of the tumors in collision. Molecular analysis of microsatellite regions was performed in different microdissected areas. Identical loss of heterozygosity (LOH) at 9p21 and 17p13 was determined in the three different microdissected areas of the adenocarcinoma component. LOH was not determined in any area of the oat cell carcinoma. This is the first study that analyzes the allele status of an esophageal collision tumor. Our findings suggest a biclonal origin for both components of the collision tumor.