STAT5B and T-cell large granular lymphocyte leukemia: Canonical STAT3 variants (Y640F, D661V, D661Y, N647I) have been identified in 40% of LGLL patients, whereas STAT5b variants (Y665F, N642H) are prevalent in specific disease subtypes as they were recently reported in up to 19% of TCRγδ LGLL and up to 55% of CD4+ LGLL cases [10,19,20].