Variation in morphological findings in PTCL-NOS. Histological features for PTCL-NOS include the following patterns: (A) monomorphic small-intermediate size cells with abundant cytoplasm, (B) monomorphic sheets of large cells, (C) neoplastic cells interspersed within a mixed inflammatory background, or (D) a lymphohistiocytic morphology characterized by small neoplastic cells within clusters of epithelioid histiocytes (termed Lennert pattern). Original magnification x200 and inset magnification x400. Adapted from Amador et al.³²