Single-agent Cobimetinib for Adults With Histiocytic Disorders

Cobimetinib will be administered at a dose of 60mg daily for 21 days on, then 7 days off, in a 28 day treatment cycle. Patients will have the option to discontinue treatment after 12 cycles and will be monitored for disease relapse for an additional 12 months. In the event that disease relapse occurs within the 12 month monitoring period, patients will restart treatment and continue on study. Upon restarting, the assessment schedule will restart at rechallenge cycle 1(RC-1) and all assessments will occur at the frequency and intervals. Cycle 1 Day 15 visits will not be required for patients that restart treatment after relapse. Participants will re-sign consent upon rechallenging.