Metastatic acral melanoma treatment outcomes: a systematic review and meta-analysis

Acral melanomas are a unique subset of melanomas occurring on the palms, soles, and nails. There is poor prognosis with surgery alone and no specific guidelines for the treatment of metastatic acral melanoma. This meta-analysis explored the systemic therapy outcomes for metastatic acral melanoma. Medline, Pubmed, EMBASE, and the grey literature were searched from 2010 to August 2020 for studies specifying the treatment outcome of metastatic acral melanoma. Studies were assessed by two investigators. A random-effects meta-analysis was performed and pooled Kaplan-Meier curves for progression-free survival and overall survival were created. Critical appraisal was performed using the Newcastle-Ottawa Scale. Nineteen nonrandomized studies were included, comprising 646 patients with acral melanomas and 1609 patients with nonacral melanomas treated with systemic therapy including chemotherapy, KIT-targeted drugs, as well as anti-CTLA-4 and anti-PD-1 checkpoint inhibitor therapy. Thirteen studies included Kaplan-Meier curves for progression-free survival or overall survival and 11 studies reported treatment responses. Patients with acral melanomas had worse prognosis than nonacral cutaneous melanoma (acral overall survival: median 15 months, 95% CI, 13.7-16.3 months; nonacral cutaneous: median 24 months, 95% CI, 22.6-25.4 months, P < 0.001). Acral melanoma patients treated with anti-PD-1 monotherapy had higher overall survival at 12 months (53%) compared with anti-CTLA-4 monotherapy (34%; P < 0.001). This study provides estimates of treatment response for metastatic acral melanoma, demonstrating low activity across a breadth of approved drug therapies, including anti-PD-1, the most active therapy in melanoma to date. Further research into treatments for metastatic acral melanoma is needed.