Immune and molecular correlates in melanoma treated with immune checkpoint blockade

Immunotherapy for metastatic melanoma has a decades‐long history, and the relatively recent use of checkpoint inhibitors has revolutionized treatment. Durable and sometimes complete remission of metastatic melanoma is now achievable in some patients who receive checkpoint‐blocking therapy. However, it is unclear why some patients fare better than others. This review highlights several molecular indicators of response to checkpoint inhibition in metastatic melanoma, focusing on tumor programmed death ligand 1 expression, major histocompatibility complex class I expression, mutational load in the tumor, and T‐cell infiltration into the tumor. In addition, clinical correlates of response, notably vitiligo and other immune‐related adverse events, can potentially shed light on the mechanisms by which checkpoint blockade may achieve such great success, particularly in melanoma. The authors propose that microphthalmia‐associated transcription factor—a key regulator of melanocyte survival, melanin production, and melanoma transformation—produces a molecular landscape in melanocytes and melanoma cells that can make melanomas particularly susceptible to checkpoint blockade and also can result in immune attack on normal melanocytes. Cancer 2017;123:2143‐53. © 2017 American Cancer Society.