Immune reactions in benign melanocytic nevi (BMN) without halo phenomenon are extremely rare, although humoral and cellular immune responses are involved in their development. Herein, we report a rare case of a patient with metastatic melanomas who showed a remarkable clinical response to nivolumab with a simultaneous prominent immune reaction in multiple BMN without halo phenomenon.
An adult woman with melanoma underwent a wide local excision and sentinel node biopsy. A left ilioinguinal lymphadenectomy was added because of a sentinel node micrometastasis. She also had dome-shaped, brown, soft nodules (≤8 mm; unchanged since puberty) on her face, shoulder, and neck, clinically diagnosed as typical BMN on initial examination.