This trial is conducted as Advanced medicine authorized by the Ministry of Health, Labor, and Welfare (MHLW) in Japan, and in in conformance with Clinical Trial Act.~PIb study is a dose-escalation study comprising two dose levels of imatinib mesylate with fixed dose of pembrolizumab to evaluate safety and tolerability and identify maximum tolerated dose/administered, and determine recommended phase 2 dose (RP2D).~In PII study, a Simon's minimax two-stage design is employed.The treatment period with the combination therapy of both studies will continue every 21 days for up to 33 cycles (approximately 2 years) as long as subjects are receiving benefit from treatment and have not had disease progression or met any criteria for study withdrawal.
This is an open-labelled single arm trial of pembrolizumab and imatinib mesylate in subjects with unresectable or metastatic KIT-mutant melanoma that are refractory to standard therapy. The phase Ib and II study will be conducted to evaluate the safety, tolerability and response rate data of this combination therapy. KIT-mutant tumors will be confirmed in previously biopsied tumors. This analysis will be done by next-generation sequencing.