Cutaneous Metastatic Melanoma Resembling a Halo Nevus, in the Setting of PD-1 Inhibition.

Malignant melanoma is a common source of cutaneous metastases and can occasionally adopt a histological appearance which mimics a primary melanocytic lesion, either benign or malignant. The authors describe a case of new cutaneous deposits of metastatic melanoma in a 70-year-old woman with a prominent admixed lymphocytic infiltrate, imparting a striking resemblance to a halo nevus. The authors believe this appearance was a direct reflection of treatment with pembrolizumab, a humanized antibody against the immune checkpoint inhibitor programmed death-1. With increasing use of immune-modulating drugs, this potential histological mimic may be seen more frequently in the future.