BTK and myeloid sarcoma: BTK occupancy in peripheral blood mononuclear cells has been used as a surrogate marker for inhibition of BTK activity by first line BTK inhibitors in cancer [2] and clinical data generated during the Phase 2 evobrutinib development program in participants with relapsing MS demonstrated a dose-dependent increase in BTK occupancy in the periphery, with a mean steady state BTK occupancy of > 95% in peripheral blood mononuclear cells [29].