Adjuvant pembrolizumab versus high-dose interferon α-2b for Chinese patients with resected stage III melanoma: a retrospective cohort study

Background Pembrolizumab has robust antitumor activity in advanced melanoma and has been approved for the treatment of melanoma in many countries. Adjuvant pembrolizumab was associated with longer recurrence-free survival (RFS) in patients with resected stage III melanoma. We herein report on the RFS outcomes of Chinese patients with resected stage III melanoma receiving adjuvant pembrolizumab in comparison to those receiving interferon α-2b (IFN-α-2b). Methods We retrospectively investigated the medical records of subjects with resected stage III melanoma with no in-transit metastases diagnosed who were treated at the Cancer Hospital of the University of Chinese Academy of Sciences and collected historical clinical data of patients receiving adjuvant IFN-α-2b therapy in our hospital. The RFS rates were evaluated using Kaplan-Meier curves, and the differences between the groups were tested using the log-rank test. Results A total of 29 patients receiving adjuvant pembrolizumab therapy and 27 patients receiving adjuvant IFN-α-2b therapy were enrolled. The median RFS was not reached (95% CI not estimable [NE]) in the pembrolizumab group and was 25 months in the IFN-α-2b group, and there was no significant difference in RFS between the pembrolizumab and IFN-α-2b groups (HR = 1.20, log-rank p = 0.75). There was no significant difference in RFS for acral melanoma between the pembrolizumab group and IFN-α-2b group (HR = 1.22, log-rank p = 0.79). For patients with IIIC or IIID melanoma, the RFS in the pembrolizumab group was also similar to that of the IFN-α-2b group (HR = 0.80, log-rank p = 0.47). The RFS for patients receiving pembrolizumab with programmed cell death ligand 1 (PD-L1)-positive tumors might tend to be longer than that for patients with PD-L1-negative tumors, but there was no significant difference between the groups (HR = 3.37, log-rank p = 0.17). High tumor mutational burden (TMB) did not reveal a trend to predict a longer RFS than low TMB in patients receiving pembrolizumab (HR = 1.63, log-rank p = 0.63). Grade 3-4 adverse events occurred in 6 (22.22%) of 27 patients in the IFN-α-2b group. Discontinuations attributed to adverse events (AEs) occurred in 2 patients treated with IFN-α-2b. Immune-related adverse events were observed in 5 (17.24%) patients in the pembrolizumab group. In the pembrolizumab group, grade 3-4 adverse events occurred in 2 (6.90%) patients, 1 of which required the discontinuation of a study drug and corticosteroid treatment. None of the patients discontinued treatment due to treatment-related or immune-mediated AEs. Conclusions Adjuvant pembrolizumab appeared to be as effective as IFN-α-2b in prolonging RFS in Chinese patients with resected stage III melanoma. Adjuvant pembrolizumab was associated with a lower rate of treatment-related AEs than IFN-α-2b. A prospective study is needed to confirm the clinical benefit of adjuvant pembrolizumab and determine dependable biomarkers.