Multiple Primary Merkel Cell Carcinomas Presenting as Pruritic, Painful Lower Leg Tumors

Merkel cell carcinoma (MCC) is a rare and highly aggressive neuroendocrine tumor of the skin which almost exclusively presents as a solitary tumor. It is most often seen on sun-exposed regions, historically almost exclusively on the head and neck, with only rare case reports on the extremities. Although recent studies have shown increased incidence with up to 20% on the extremities, here we present one of these rare emerging presentations, with the addition of a unique treatment option. Our patient is an 80-year-old male with a 3-month history of multiple raised, rapidly enlarging tumors on the right ankle. Two separate biopsies were performed and demonstrated sheets and clusters of small blue cells filling the dermis with scant cytoplasm, dusty chromatin, and nuclear molding. Subsequent immunohistochemical stains confirmed the diagnosis of multiple primary MCC. Despite the characteristic immunohistochemical profile of primary MCC, the possibility of a metastatic neuroendocrine carcinoma from an alternate primary site was entertained, given his unusual clinical presentation. A complete clinical workup including CT scans of the chest, abdomen, and pelvis showed no evidence of disease elsewhere. Instead of amputation, the patient opted for nonsurgical treatment with radiation therapy alone, resulting in a rapid and complete response. This case represents an unusual presentation of primary MCC and demonstrates further evidence that radiation as monotherapy is an effective local treatment option for inoperable MCC.