A unique subgroup within PTCL-NOS with features of cytotoxic T-cells (CT-PTCL). (A) Hierarchical clustering of the PTCL-NOS group demonstrated a distinct cluster of 11 cases that also clustered together when SOM and KM were used. (B) Gene signature associated with CT-PTCL was highly expressed in activated CD8⁺ T cells. (C) GSEA analysis identified enrichment of CD8⁺ T-cell and other gene signatures. The enrichment score curves were obtained from GSEA software. Vertical black lines indicate the position of the enriched genes (Hit) comprising the gene set. The graph on the bottom of each panel shows the ranked list metric (signal-to-noise ratio) for each gene as a function of the rank in the ordered dataset (see Subramanian et al²⁷  for more details). (D) Kaplan-Meier plots of OS and EFS of CT-PTCL and the remaining PTCL-NOS cases indicating poor prognosis of CT-PTCL. (E) A representative CT-PTCL case was immunostained for Granzyme B (original magnification 200× for both panels).