Representative morphologic patterns in PTCL subtypes. PTCL-GATA3 was significantly associated with a monomorphic, monotonous, tumor cell–rich morphology with a minimal inflammatory background characterized by: (A) small-intermediate cells with abundant cytoplasm (pattern 1) or (B) clusters or sheets of large cells (pattern 2). In contrast, PTCL-TBX21 was significantly associated with a polymorphous morphology, characterized by (C) neoplastic cells interspersed in a mixed inflammatory background (pattern 3) or (D) the classic lymphohistiocytic (Lennert) lymphoma morphology composed of small tumor cells within clusters of epithelioid histiocytes (pattern 4). (E) Distribution (percentage) of morphological patterns in the 2 PTCL subtypes with monomorphic patterns associated with PTCL-GATA3, whereas polymorphic patterns associated with PTCL-TBX21 (P < .001). (F) The monomorphic patterns (1 and 2) and the Lennert lymphoma pattern (pattern 4) were associated with worse OS, when both cohorts were combined. (A-D) H&E stain; original magnification ×200; inset magnification ×400.