Adjuvant Anti-PD-1 Monotherapy Versus Observation for Stage III Acral Melanoma of the Sole: A Multicenter Retrospective Study in Japanese Patients

Adjuvant anti-PD-1 (adj PD-1) antibodies are extensively used to improve survival in patients with resected melanoma. Clinical trials on adj PD-1 antibodies have revealed significant improvements in recurrence-free survival (RFS); however, few of these trials have included patients with acral melanoma (AM).

Clinical data were retrospectively collected from Japanese patients who underwent resection of stage III sole AM between 2014 and 2021. Survival outcomes, including RFS, distant metastasis-free survival (DMFS), and overall survival (OS), were compared between patients without adjuvant therapy (OBS group) and those receiving adj PD-1 group.

This study included 139 patients (OBS: 79; adj PD-1: 60), with a median follow-up of 2.6 years. The baseline characteristics were comparable, except for age and nodal metastasis. No significant differences in survival were observed between the OBS and adj PD-1 groups (3-year RFS: 36.7% v 27.5%, P = .13; 3-year DMFS: 51.0% v 45.3%, P = .51; 3-year OS: 65.3% v 67.4%, P = .45). Multivariate analysis showed no survival benefit of adj PD-1 (RFS: hazard ratio [HR], 1.25, P = .29; DMFS: HR, 1.03, P = .89; and OS: HR, 0.69, P = .23). Each survival outcome after propensity score matching confirmed no significant difference between the matched OBS group (n = 52) and adj PD-1 group (n = 52; 3-year RFS: 34.3% v 25.9%, P = .22; 3-year DMFS: 45.6% v 46.5%, P = .85; 3-year OS: 60.7% v 68.9%, P = .29).

Adj PD-1 did not improve the prognosis in sole AM. However, further studies are essential to evaluate the efficacy of the adj anti-PD-1 antibody in AM.