Involution of selective melanocytic lesions in a 79 year-old male with metastatic melanoma on immunotherapy

A 79 year-old man presented for naevus surveillance by Vectra imaging, after being diagnosed with a metastatic melanoma with no identified primary lesion. A subcutaneous thigh nodule had been biopsied for diagnosis based on an inconclusive ultrasound scan. CT PET scan showed metastatic disease in the left thigh and lungs, so the patient was referred to oncology.
He presented to our imaging study with no prior full skin examination, and demonstrated a 20 x 15mm atypical pigmented lesion on his right chest wall representing most probably the primary melanoma. The patient started immunotherapy with pembrolixumab the next day, and was reimaged four months into his treatment. Several of his naevi and lentigines, including the suspected primary melanoma, had involuted partially. The case interestingly demonstrates the rapid partial involution of selective melanocytic lesions due to immunotherapies.
This research was conducted with the support of the Centre of Research Excellence for the Study of Naevi, funded by the National Health and Medical Research Council (NHMRC; grant ID: APP1099021).

Dr. Stephen Thomas