Background: Immune checkpoint inhibitors (ICI) have transformed treatment for patients (pts) with advanced melanoma, as have BRAF/MEK inhibitors for pts with BRAF V600-mutant melanoma. However, pts with acral or mucosal melanomas are in particular need of more options given a lower objective response rate (ORR) to ICI, and lower incidence of BRAF V600 driver mutation. Such BRAF mutations are found in only 5-10% of acral/mucosal melanomas, while KIT mutations/amplifications are found in 10-20%. Even when present, a KIT alteration does not guarantee response to KIT inhibition, with only about one-third responding as previously shown in 3 phase II studies. A significant number of KIT-mutant melanomas have been shown to demonstrate NF1 or SPRED1 loss, with recent preclinical work showing that such alterations are associated with the loss of negative suppression of RAS, resulting in RAS activation and MEK dependence. We hypothesize that NF1 or SPRED1 loss cooperates with KIT mutations to drive melanomagenesis and resistance to KIT inhibition, and propose to target this vulnerability with a combination approach to targeted therapy. This phase II study will be the first to evaluate the efficacy and safety of binimetinib plus imatinib in pts with KIT-mutant melanoma. Methods: This is an investigator-initiated phase II study of binimetinib in combination with imatinib in pts with BRAF V600 WT, KIT-mutant unresectable melanoma who have progressed on or who are ineligible for ICI (NCT04598009). Pts will be ≥18 yo with performance status ECOG 0-2, and have unresectable Stage IIIB/C/D or Stage IV melanoma that is BRAF V600 WT and KIT-mutant by CLIA-certified testing platform. Pts will have progressed on prior ICI or other standard-of-care (SOC) therapies, or be ineligible for or unable to tolerate SOC therapies. Pts with brain metastasis will be eligible if clinically stable and determination made that no CNS-specific treatment is required prior to study start. Pts previously treated with a MEK inhibitor will be excluded. A Simon 2-stage Minimax design will be used; the null hypothesis that the true response rate is 0.1 will be tested against a one-sided alternative. 15 pts will be accrued in the first stage. If there are £1 responses, the study will be stopped. Otherwise, 10 additional pts will be accrued for a total of 25. The null hypothesis that the true response rate is 0.1 will be rejected if ≥6 responses are observed. This yields a type I error rate of 0.05 and power of 0.8017 when the true response rate is 0.3.Primary endpoint: ORR (RECIST). Secondary endpoints: duration of response, progression-free survival, overall survival, clinical benefit rate (CR, PR, or SD ≥16 weeks), safety profile (CTCAE). Exploratory objectives to include investigations of association between clinical response and baseline NF1 and SPRED1 status, and of pathologic correlates of acquired resistance. Study began enrolling pts in December 2020 and is ongoing. Clinical trial information: NCT04598009