Western blotting studies revealed inhibition of phosphorylation and activation of STAT1, STAT3 and STAT5 signalling in the SS cells harbouring both JAK1 mutations, whereas the mature T-cell lymphoma-derived cell line, HH, which does not carry mutations in the JAK–STAT axis, did not show any changes (Fig. 4d; Supplementary Fig. 12). Here, STAT5B is linked to synovial sarcoma.