Cutaneous Eruption Secondary to Immunotherapy for Metastatic Melanoma Limited to Sites of Locoregional Melanoma Metastases: A Possible Variant of Locus Minoris Resistentiae

Immune checkpoint inhibitor therapies targeting PD-1 or CTLA-4 (programmed cell death 1 or cytotoxic T-lymphocyte–associated 4 protein) are increasingly used to treat metastatic melanoma.¹ The most common adverse event from these classes of drugs is cutaneous toxic effects.^1,2 The mechanism is incompletely understood but thought to be mediated by CD4-positive and CD8-positive T cells activated by immunotherapy.³ Immunotherapy-induced cutaneous eruptions include discrete or generalized papules without regional preference or, rarely, in inverse distribution. We report 2 cases of patients with metastatic melanoma who developed spongiotic cutaneous eruptions limited to the region of their melanoma locoregional metastases.