Cobimetinib in Newly Diagnosed or HMA-treated CMML Patients With RAS Pathway Mutations

This is an open-label, nonrandomized phase 2 trial to assess the efficacy of cobimetinib in RAS pathway activated CMML. Two cohorts of patients will be accrued using Simon's two-stage design (Simon, 1989) for both cohorts. Cohort 1 will enroll nine newly diagnosed patients in the first stage and if four or more responses are observed five additional patients will be enrolled in the second stage. Cohort 2 will enroll six HMA refractory patients in the first stage and if one or more responses are observed then nine additional patients will be enrolled in the second stage. All eligible patients will be treated daily with cobimetinib in 28-day cycles. Cobimetinib will be administered consecutively for three weeks followed by a one week break prior to the start of the following cycle. Patients will remain on study therapy until treatment discontinuation criteria is met.