BTK and myeloid sarcoma: MS is a chronic, immune-mediated disease of the CNS, leading to demyelination and axonal damage.13 This translates into clinical disability for people living with MS.13,14 Second-generation BTK inhibitors are under clinical development for relapsing MS (RMS), relapsing-remitting MS (RRMS), primary progressive MS (PPMS) and one in secondary progressive MS (SPMS), summarized in Table 1.