STAT5B and mature T-cell and NK-cell non-Hodgkin lymphoma: STAT5B N642H has further been identified in multiple subtypes of PTCL: 2% of cases of T-LGL, 7/21 (33%) of cases of HSTL, and in T-PLL where it has demonstrated increased colony forming capacity in Jurkat cells, a T-cell leukemia cell line [8, 12, 47].