Abstract: Merkel cell carcinoma (MCC) is a rare and highly aggressive cutaneous neuroendocrine carcinoma. To date only 16 cases of MCC associated with arsenic exposure have been reported in the literature. The patient in this case was a 73-year-old male who presented with multiple cutaneous tumors all over the body, accompanied by repeated ulceration and exudation for more than 7 years. Seven years prior, he had a history of topical application of arsenic sulfide-containing ointment. Dermatological examination revealed multiple deep yellow keratotic papules on the basis of extensive hyperkeratosis of the palms and soles, scattered pigmented macules on the entire skin, and an elevated tumor under the umbilicus with clear boundaries and eroded exudation on the surface. Multiple grayish-white rough areas were observed on the skin of the left knee, upper and lower segments of the right thigh, which were prone to bleeding on palpation with mild tenderness. The diagnosis of arsenic keratosis, abdominal MCC, and multiple squamous cell carcinoma of the lower extremities was confirmed by histopathological examination.

Key words: Merkel cell carcinoma, arsenical keratosis, squamous cell carcinoma