Atypical late presentation of muscular metastasis of melanoma in the contralateral limb.

A man in his 50s presented to plastic surgery again with a lesion on his left upper arm. He had previously been treated for a malignant melanoma (MM) on his right arm over 5 years earlier. Sentinel lymph node biopsy (SLNB) had been negative, and he had completed the recommended 5 years follow-up period. Imaging was suspicious for an intramuscular soft tissue malignancy within the triceps muscle. After discussion with the regional sarcoma service, a core biopsy was performed. Histopathology suggested a diagnosis of metastatic MM, which was confirmed after surgical excision. This case highlights a rare example of an isolated muscular metastasis of MM, which presented at a distant site, over 5 years from the original treatment. This case highlights the unpredictable nature of MM, reminding clinicians of the need for a low threshold for investigation of soft tissue masses in patients with a history of cutaneous malignancy.