A white man in his early 40s with a medical history of chronic lymphocytic leukemia (Rai stage 0) reported a 6-month history of a growing mass in his right axilla and weight loss. Physical examination revealed palpable right axillary lymphadenopathy. The patient was an active smoker (1 pack per day) with an unremarkable family history. A positron emission tomography scan showed a hypermetabolic right axillary lymph node that measured 5 × 5 cm as well as multiple liver lesions, the largest of which measured 8 cm. The results of a core needle biopsy specimen from the right axillary lymph node were consistent with malignant neoplasm, with immunohistochemistry staining positive for S100, HMB-45, and MART-1. He began pembrolizumab therapy.