Scalp melanoma with rectus abdominis metastasis: A rare case report.

Rationale: The main cause of death in melanoma patients is widespread metastases as it can metastasize to almost every organ. However, melanoma skeletal muscle metastases (MSMM) are exceptional, and only a few cases of MSMM to the rectus abdominis muscles have been previously described. And our case maybe the first reported case in Asia region.

Patient Concerns: A 45-year-old man with history of right scalp melanoma, pT3aN0M0, stage IIA status post wide excision with 2 cm safe margin and right neck lymph node dissection at 5 years before. He had an almost 5 years disease-free period but presented to our clinic due to intermittent abdominal sharp pain for 1 to 2 months, with a palpable soft tissue mass over his right abdomen. Metastatic melanoma to rectus abdominis muscles was highly suspected.

Interventions: The patient subsequently underwent radical en-block extraperitoneal 15 cm segmental resection of the right rectus abdominis muscle including tumor mass. The resected tumor was a black-gray colored solid mass, and the final histologic study showed a metastasis of melanoma.

Outcomes: Postoperative course of the patient was uneventful, and the right abdominal pain was improved. The patient was referred for further target therapy, but passed away half a year later due to multiple metastasis.

Lessons: Scalp melanoma with isolated rectus muscle metastasis is extremely rare especially for a young aged patient who had an almost 5-year disease-free period. Surgery is a potentially curative therapy for patients with isolated metastatic melanoma. The goal is negative resection margins, in order to avoid local recurrences. Radical compartmental surgery should be considered for selected stage IV melanoma patients with sole rectus abdominis MSMM, whose disease could be amenable to complete resection, in preliminary procedure to prolong disease-free survival time. For oligometastatic disease, surgical resection is sometimes useful in carefully selected patients after systemic therapy; also, it could be performed as symptomatic treatment.