Background It is common that patients with head and neck cancers have secondary malignant neoplasm of esophageal cancer. Methods To know the genetic background of the development of these secondary cancers, we performed microsatellite assay at six loci and immunohistochemical analysis on head and neck cancers of eight patients with esophageal cancer and on those of 19 patients without esophageal cancer. Results Replication error (RER) at more than two loci was observed in two (25%) of eight double cancer patients, whereas it was not observed in the patients without the secondary cancer. Immunohistochemically, overexpression of cyclin D1 was detected in two (25%) of eight double cancer cases and in two (11%) of 19 non-double cancer cases, respectively, the incidence showing a higher tendency in the former. Conclusions The results suggest that microsatellite instability may be implicated in the development of head and neck double cancers and that RER (+) phenotype may serve as a biomarker to predict the development of secondary esophageal cancer in patients with head and neck cancer.
