A phase II study on the efficacy of regorafenib in treating patients with c-KIT-mutated metastatic malignant melanoma that progressed after previous treatment (KCSG-UN-14-13)

Background: c-KIT mutations are found in approximately 15% of patients with malignant melanoma in the Asian population. Regorafenib, an oral multikinase inhibitor, acts against both wild-type and mutant KIT. Objective: This multi-institutional, phase II, single-arm study aimed to evaluate the efficacy of regorafenib against metastatic malignant melanoma harbouring c-KIT mutations. Methods: Patients with metastatic melanoma positive for c-KIT mutations, upon progression after at least one line of systemic treatment, were enroled. Patients received oral regorafenib 160 mg once daily for 3 weeks (4-week cycle). The primary endpoint was disease control rate (DCR), and secondary endpoints were safety, overall response rate (ORR), progression-free survival (PFS), and overall survival (OS). Results: In total, 23 patients were enrolled. c-KIT mutations were frequently reported in exon 11 (14/23, 60.9%), followed by exons 13, 17, and 9 in 5 (21.7%), 5 (21.7%), and 2 (8.7%) patients, respectively. DCR at 8 weeks was 73.9%, with 2 patients (8.7%) achieving complete response, 5 (21.7%) achieving partial response, and 10 (43.5%) showing stable disease. ORR was 30.4% (7/23). The median follow-up period was 15.7 months (95% confidence interval [CI], 9.6–21.3), and median OS and PFS were 21.5 months (95% CI, 15.1–27.9) and 7.1 months (95% CI, 5.0–9.2), respectively. Circulating tumour DNA analysis in selected patients showed high c-KIT correlation (85.7%) with tissue-based tumour mutational profiles. The most common adverse events (AEs) were skin reactions, including palmar-plantar erythrodysesthesia (52.2%), and grade 3 AEs were reported in 39.1% (9/23) of the patients. Conclusion: Regorafenib in second- or later-line settings demonstrated significant activity in patients with metastatic melanoma harbouring c-KIT mutations.