Background: Clinical data on PD-1 inhibitor combined with interferon in metastatic melanoma treatment were still limited. The objective of this study was to assess the efficacy and safety of PD-1 inhibitor/interferon-α1b combination therapy for Chinese metastatic melanoma patients in the real world. Methods: We reviewed patients diagnosed as metastatic melanoma and had received PD-1 inhibitor (pembrolizumab, 2 mg/kg, every 3 weeks, intravenously or toripalimab 240mg every 2 weeks, intravenously) combined with interferon-α1b(10μg/kg, every other day, subcutaneously) in Xijing Hospital from Dec 2018 to Nov 2020. Efficacy and safety profiles were evaluated using Response Evaluation Criteria in Solid Tumors version 1.1 and Common Terminology Criteria for Adverse Events version 5.0, respectively. Results: In total 65 patients were reviewed in this study, including 13 cases with ECOG performance status ≥2. Acral and mucosal cases accounted for 47.7% and 23.1% respectively. In 27(41.5%) patients, the combination therapy was used as the first line treatment, whereas in the rest 38 patients as second or subsequent lines. The median follow-up period was 8 months (1.5-21 months). Median OS was 15 months (95CI%: 10.62-19.38 months). Median PFS was 6 months (95CI%: 2.54-9.46 months). 6-month and 1-year PFS rate were 48.1% and 35.3%. 6-month and 1-year OS rate were 80.9% and 59.8%. Objective response was seen in 18.46% cases, with 12.31% of patients exhibiting ongoing response. The best confirmed disease control rate was 73.85%. Multivariate analysis demonstrated that overall survival was significantly associated with ECOG performance status ≥2 (OR=3.32，95%CI=1.14-9.66 ), regardless of age(≥65), elevated LDH, PD-1 inhibitor type and the line of the combination therapy. Select treatment related AEs (TRAEs) of any grade were observed in 57(87.69%) patients. The leading 3 TRAEs were lymphopenia, fatigue and fever. Grade 3 to 4 TRAEs were recorded in 2 cases. Grade 4 hyponeutrophilia occurred in a patient with ECOG status 3 using interferon-α1b plus toripalimab and resulted in discontinuation of both PD-1 inhibitor and IFN-α1b. Grade 3 headache was reported by one patient using interferon-α1b plus pembrolizumab and was solved with celecoxib 200mg daily. No drug-related deaths were reported. Conclusions: PD-1 inhibitor combining interferon-α1b therapy shows promising efficacy and acceptable toxicity in this real-world cohort of Chinese metastatic melanoma patients.

*1 patient with compeleted response received vemurafenib 960mg twice daily besides the combination therapy.