In psoriasis, another Th17-mediated disease, blockade of STAT3 or its associated Janus kinases have already been discussed as potential treatment options.37,38 In MS, higher levels of phosphorylated STAT3 were observed in PBMCs from patients during relapse or after in vitro activation.39,40 Furthermore, polymorphisms in the corresponding gene locus are associated with enhanced risk of MS.41 In considering therapeutically targeting STAT3, its broad signalling function in immune and also non-immune cells needs to be kept in mind. Here, STAT3 is linked to myeloid sarcoma.