Mutations in the SH2 domain of STAT3 have been identified across several types of lymphomas: Y640F, D661Y, D661I, D661H, G618R, S614R, and N647I in T-LGL; Q743H in PTCL; D661Y, D661H, N647I, G618R, S614R, and N647I in ALCL; Y640F and I498Y in cutaneous T-cell lymphoma (CTCL); and D661Y, D661H, S614R, and A703T in NKTCL.599 Numerous mutations within STAT5b have been observed across various malignancies, including N542H detected in TLGL, NKTCL, and CTCL, Y665F exclusively in TLGL and NKTCL, Q706L in CTCL, T-ALL, and T-PLL. This evidence concerns the gene STAT5B and primary cutaneous T-cell non-Hodgkin lymphoma.