Histologic Features of Melanocytic Nevi Secondary to Melanoma Treatment With Immune Checkpoint Inhibitors

Programmed death-1 (PD-1) inhibitors are anticancer drugs that function as immune checkpoint blockers, targeting PD-1 proteins on the surface of cells to restore immune system activity against tumors. While cutaneous adverse events associated with immune checkpoint inhibitor therapy are well documented, this case highlights the reactive histopathologic changes that can occur in benign nevi during treatment. Here, we present the case of a 51-year-old Hispanic female with a history of melanoma on the chest who was seen in clinic for routine follow-up. Three suspicious pigmented lesions located on the right upper back, abdomen, and left shoulder were biopsied for further analysis. Histopathologic examination indicated an intradermal melanocytic nevus with irritation and inflammation, an inflamed, mildly dysplastic compound melanocytic nevus, and a compound melanocytic nevus with marked inflammation and no atypia. Additional clinical history revealed that the patient was receiving treatment for advanced melanoma with immune checkpoint inhibitors. Increased awareness of these features in melanocytic lesions associated with PD-1 and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors may help with accurate diagnosis.