Merkel cell carcinoma in a young man with AIDS-related Kaposi sarcoma

Merkel cell carcinoma (MCC) is a rare, aggressive primary neuroendocrine carcinoma of the skin that can present in immunocompromised patients. Kaposi sarcoma (KS) is an indolent angioproliferative tumor associated with human herpesvirus 8 (HHV8). The concurrence of both MCC and KS is rare, and there have been limited cases reported in the literature. We present a rare case of concurrent MCC and KS in an immunocompromised patient. To our knowledge, this is the first report of MCC and KS described in the same histopathological specimen. A 37-year-old Black male with a history of recurrent AIDS-related KS involving bilateral lower extremities was evaluated for a tender nodule on the left posterior leg. A punch biopsy was consistent with MCC. Magnetic resonance imaging brain and full-body positron emission tomography/computed tomography (PET/CT) scan were without evidence of distant metastasis. The patient underwent wide local excision with negative margins and completed postoperative radiation therapy. However, he later developed cutaneous metastasis of MCC to the left medial thigh and excision revealed residual MCC with adjacent KS. Treatment is still ongoing with pembrolizumab for both KS and MCC.