Merkel cell carcinoma, Bowen's disease and chronic occupational arsenic poisoning.

We diagnosed a unique case of Merkel cell carcinoma (MCC) coexisting with Bowen's disease on the sole of the foot of a 72-year-old man who had worked for about 4 years in a factory handling inorganic arsenic. He had a past history of arsenical keratosis and multiple Bowen's disease. The tumour first appeared as a reddish macule and then showed marked growth over the next month. The tumour was excised and the specimen was examined histopathologically. The tumour consisted of two components: a group of atypical cells representing Bowen's disease in the epidermis and another group of atypical cells with a trabecular pattern characteristic of MCC in the dermis. Neither group of cells showed transitional findings, and the tumour elements were divided by a clear basement membrane. The tumour cells in the dermis were positive for neurone-specific enolase, and on electron microscopy had dense core granules in the cytoplasm. Inorganic arsenic can cause various cutaneous neoplasms, but to our knowledge, this is the first report of a case of MCC associated with Bowen's disease.