Peripheral T‐cell lymphoma, not otherwise specified (PTCL NOS) is classified into two prognostic subtypes, PTCL‐TBX21 and PTCL‐GATA3, using an immunohistochemistry (IHC) algorithm based on TBX21/CXCR3 and GATA3/CCR4 expression. The gene discussed is GATA3; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.