Pigmented epithelioid melanocytoma

A 16‐year‐old Hispanic male presented with a nontender purple nodule on the right shoulder that had been present for 1 year. There was no personal or family history of skin cancer. He had no significant past medical history. Physical examination revealed a 10 mm × 5 mm, firm, dark purple nodule on the right anterior shoulder ( Fig. 1). The surface was not eroded or crusted. The nodule was not attached to underlying structures. A deep shave excision was performed. 1Clinical photograph of tumor of the right anterior shoulder Microscopic examination showed a polypoid tumor composed of heavily pigmented epithelioid melanocytes and melanophages with collagenous stroma ( Figs 2 and 3). Clusters of tumor cells were seen within the papillary dermis to lie in close apposition to the epidermis, which was variably hyperplastic and attenuated, but the lesion was predominantly dermal with only occasional atypical melanocytes disposed singly along the basal layer. The lesion appeared well circumscribed and, although quite thick at 3.42 mm, extended only superficially into the reticular dermis, the thickness being largely the result of protuberant growth. The nuclear detail was obscured by the copious melanin, and a bleached preparation was also examined. These sections revealed only mild cellular atypia, with round nuclear contours, open chromatin with peripheral margination, and a single distinct but small nucleolus; cytoplasm was abundant and no mitotic figures were identified. Ulceration, significant host lymphocyte response, lymphovascular invasion, and microsatellitosis were also absent. The diagnosis of animal (equine)‐type melanoma was favored over other pigmented nevomelanocytic lesions, including cellular blue nevus, blue nevus with hypercellularity, and regressive tumoral melanosis. 2Low‐power histopathology of biopsy specimen (hematoxylin and eosin, ×10)3High‐power histopathology of biopsy specimen (hematoxylin and eosin, ×100) Complete physical examination performed at the next follow‐up visit revealed no lymphadenopathy or organomegaly. Serum lactate dehydrogenase and chest radiographs were normal. The patient underwent lymphoscintigraphy ( Fig. 4) followed by wide local excision (2 cm margins), intraoperative lymphatic mapping, and sentinel lymph node biopsy ( Fig. 5) 3 weeks after the initial biopsy. Three sentinel lymph nodes were identified in the right axilla and excised. All were grossly negative for tumor. Microscopic examination, however, showed two of the nodes to harbor subcapsular and intraparenchymal tumor deposits ( Fig. 6), which were immunoreactive for S‐100 protein and Mart‐1. Computed tomography scans of the chest, abdomen, and pelvis did not demonstrate metastatic disease. Complete axillary lymph node dissection was recommended, but the patient and his family declined. At 6 months after the patient's initial diagnosis, he was free of any overt metastatic disease. 4Lymphoscintigraphy5Sentinel lymph node ( in vivo )6Sentinel lymph node (hematoxylin and eosin, ×25)