Skeletal muscle and solitary bone metastases from malignant melanoma: multimodality imaging and oncological outcome.

Malignant melanoma solitary metastases to bone or skeletal muscle occur in 0.8% of patients. The aim of this study was to evaluate features of skeleton and muscle metastases with multimodality imaging and review the oncological outcome. Thirteen patients with melanoma metastases from January 2006 to February 2016 were included. Histologic confirmation was obtained. Imaging studies included computed tomography (CT), MRI, and/or positron emission tomography/CT. Treatment received and BRAF status were recorded. Differences in BRAF status and overall survival (OS) were analyzed using the χ-test. Associations between OS and metastases were analyzed using Cox proportional models. Nine (69%) patients showed osseous involvement. Lower extremity bones were affected in three (23%) patients: first toe, right calcaneal spurs, and knee. The spine was involved in three (23%) patients. In two (15%) patients, the pelvic bones were involved. In one (8%) patient, the temporal bone was affected. Nine (70%) patients had a history of malignant melanoma, with a median time to progression of 28 months. The median OS was 18 months: 24 months in patients with a history of melanoma and 3 months in patients with metastases at first diagnosis. The median follow-up duration was 28 months. BRAF mutant versus wild-type tumors showed significant differences in OS (P=0.03). The hazard ratio for death in the metastatic group at diagnosis was 6.83, 95% confidence interval: 1.060-144.072 (P=0.04). Solitary metastases from melanoma to the skeleton and muscle are rare. CT, MRI, and positron emission tomography/CT are useful for the evaluation of musculoskeletal findings. Image findings are not definitive for diagnosing a malignant solitary lesion; thus, a pathologic confirmation with a biopsy is recommended.