Several of these studies have revealed a recurrence of activating, oncogenic mutations in the JAK/STAT signaling pathway, specifically in the signal transducer and activator of transcription (STAT) STAT5B and STAT3 transcription factors, in multiple subtypes of PTCL [11, 15, 20–28]. Here, STAT5B is linked to mature T-cell and NK-cell non-Hodgkin lymphoma.