STAT5B and T-cell large granular lymphocyte leukemia: Intriguingly, each of the described loss-of-function germline STAT5B mutation is private, while reported somatic, heterozygous, STAT5B gain-of-function mutations associated with large granular lymphocytic leukemia or distinct types of T- or NK- lymphomas are clustered, often with the same mutation found in more than one individual15–17,47–49.