Cellular blue nevus simulating metastatic melanoma: report of an unusually large lesion associated with nevus-cell aggregates in regional lymph nodes.

A young Caucasian woman had a large area of blue-gray discoloration on the flank and palpable axillary lymph nodes. The discolored area had enlarged during a recent pregnancy, contained multiple subcutaneous nodules, demonstrated increased cellularity and mitotic activity, and was associated with an axillary lymph node containing black streaks within the capsule. Although the lesion was initially considered to be a metastatic malignant melanoma, re-evaluation showed it to be a benign cellular blue nevus with benign nevus-cell aggregates within a regional lymph node. We report this case to emphasize how cellular blue nevus can simulate malignant melanoma and to increase physician awareness of this benign variant of melanocytic nevus so that inappropriate surgery and chemotherapy can be avoided.