Whilst the STAT3 Y640F mutation was distributed across T-cell NHL cases, specifically 7 ATLL, 1 NK/T-cell lymphoma (NKTCL) and 1 MF, the IRF4 K59R mutation was only seen in ATLL patients, consistent with the restriction of signature 17 to these patients. Here, STAT3 is linked to adult T-cell leukemia/lymphoma.