In accordance with the observation that in other T-cell-derived neoplasms, STAT5B mutations tend to correlate with aggressive diseases while STAT3 mutations occur at high frequency in indolent leukaemias24, 28, 41, interestingly, in EATL-II, the very high prevalence of STAT5B alterations also contrasts with the absence of STAT3 mutations. Here, STAT5B is linked to enteropathy-associated T-cell lymphoma.