Basha BM, Bryant SC, Rech KL, et al. - Researchers examined an immunohistochemical panel of 5 T-follicular helper (TFH) markers (CD10, BCL6, PD-1, CXCL13, and ICOS) for its utility for identification of TFH phenotype in angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphoma (PTCL) not otherwise specified (NOS). Twenty-two cases of AITL and 29 cases of PTCL-NOS were assessed immunohistochemically for the 5 markers. Expression of ≥ 2 TFH markers was observed in all AITL cases. Reclassification of 41% PTCL-NOS cases to PTCL-TFH was made using this panel. For the TFH phenotype, they observed a positive percent agreement of 97% for PD1, 94% for ICOS, 44% for CD10 and CXCL13, and 29% for BCL6 and a negative percent agreement of 100% for CD10, BCL6, and CXCL13, 82% for ICOS and 71% for PD1. Relative to PTCL-TFH cases, AITL cases more frequently contained expanded CD21-positive follicular dendritic cell meshworks, clear cell cytology and polymorphous inflammatory background; however, a significant Kruskal-Wallis trend was observed in all morphologic variables between the 3 groups suggesting a continuum from PTCL-NOS to PTCL-TFH to AITL. They also observed a significant correlation of the median number of morphologic features of AITL with the number of TFH markers positive (Spearman coefficient ρ = 0.759). Findings thereby suggest a possible impact of the stain panel chosen on cases classified as PTCL-TFH. Existence of this entity along a spectrum between PTCL-NOS and AITL was suggested.