Malignant melanoma arising within nevus spilus.

A 68-year-old Caucasian man presented with a suspicious lesion near the left axilla during a full skin examination that was performed for a presentation for dermatitis. The patient stated that he had the lesion for several decades but that it may have become more raised over the past few months. He did not think much of the changes, however, because it was to him, "just a birthmark." The patient had no personal or family history of melanoma. On examination, the patient had a 4.5-cm by 1.2-cm oval light tan patch studded with multiple hyperpigmented macules regularly distributed within the lesion. In addition, at the lateral aspect of the lesion, the patient had a 0.9-cm irregularly pigmented black papule that was suspicious for melanoma (Figure 1). A deep saucerization biopsy of the lesion was performed, and histopathological examination revealed malignant melanoma, with a Breslow depth of 1.13 mm (Figure 2 and Figure 3). It was recommended that the patient have a wide local excision of the biopsy site and the adjacent remaining portions of the nevus spilus. A sentinel lymph node biopsy and an oncologic evaluation were also performed. The sentinel lymph node biopsies, as well as a computed tomographic scan performed by oncology, showed no evidence of metastatic disease. Since the procedure, the patient has shown no signs of disease recurrence.