STAT3 and primary cutaneous T-cell non-Hodgkin lymphoma: In the early stages of CTCL the IL-2Rgc-signaling cytokines IL-2, IL-4, IL-7, IL-15, and IL-21 activate STAT3 and/or STAT5, thus promoting malignant cell proliferation and survival [6–9] (and reviewed in ref. 4).