Clinical Activity of Ipilimumab in Acral Melanoma: A Retrospective Review.

BACKGROUND: Ipilimumab improves overall survival (OS) in advanced melanoma. Acral melanoma is an uncommon clinical subtype of this disease associated with poor prognosis. The clinical activity of ipilimumab has not been well-defined in advanced acral melanoma.

METHODS: We retrospectively reviewed the demographics, treatment history, and clinical outcomes for all patients with acral melanoma treated with ipilimumab from two academic centers between February 2006 and June 2013. Using Cox proportional hazards models, we assessed for factors that correlated with OS.

RESULTS: A total of 35 patients with acral melanoma received ipilimumab. Melanomas arose on volar surfaces (n = 28) and subungual sites (n = 7); stage M1c disease was present in 54%, and 45% had elevated serum lactate dehydrogenase (LDH). Best response by RECIST 1.1 criteria was complete response in 1 patient, partial response in 3, and stable disease (SD) in 4 for an objective response rate (ORR) of 11.4% and a clinical benefit rate (ORR + SD) at 24 weeks of 22.9%. Median progression-free survival was 2.5 months (95% confidence interval [CI]: 2.3-2.7 months); median OS was 16.7 months (95% CI: 10.9-22.5 months). Normal LDH and absolute lymphocyte count ≥1,000 at 7 weeks predicted longer OS. Immune-related adverse events (irAEs) were noted in 16 patients including 7 with grade 3/4 irAEs (20%).

CONCLUSION: Ipilimumab is clinically active in acral melanoma with similar ORR and OS compared with unselected melanoma populations. Ipilimumab remains a viable therapeutic option for patients with advanced acral melanoma.

IMPLICATIONS FOR PRACTICE: Ipilimumab is a commonly used immune therapy that improves survival in metastatic melanoma. The clinical activity of ipilimumab in certain rare melanoma subtypes, such as uveal or mucosal melanomas, is suboptimal. Acral melanoma is another unusual subtype of this disease that arises on the palms, soles, and nailbeds. In this study of 35 patients with acral melanoma from 2 centers, ipilimumab was found to have activity that appears equivalent to unselected melanoma (response rate of 11.4%, median overall survival of 16.7 months). Ipilimumab remains a viable treatment option for this melanoma subpopulation.