Merkel cell carcinoma associated with bowenoid actinic keratosis

An sl-year-old woman developed a rapidly growing nodule on the erythematous plaque of her left cheek. Histologically, tumor nests were located in the dermis without epidermal connection. The tumor nests were mainly composed of small-sized cells with round to oval nuclei and scanty ill-defined cytoplasm, Epidermis showed acanthosis with elongation of the rete ridges, and in this portion some atypical cells and multinucleated cells were observed. Infiltration of mononuclear cells and basophilic degeneration were also observed in the dermis. Immunohistochemical studies disclosed that the tumor cells were positive for neuron-specific enolase but negative for S-100 protein. Electron microscopic studies disclosed scattered, round, membrane bound granules with dense cores in the cytoplasm of tumor cells. We diagnosed this case as Merkel cell carcinoma developed in the lesions of bowenoid actinic keratosis. This case supports a hypothesis that actinic damage may contribute to the development of Merkel cell carcinoma of the skin.