LAUSR

Peripheral T-cell lymphoma (PTCL) is a heterogeneous group of mature T-cell malignancies with approximately one-third of cases designated as PTCL-not otherwise specified (PTCL-NOS). Using gene expression profiling (GEP), we have previously defined two major molecular subtypes of PTCL-NOS; PTCL-GATA3 and PTCL-TBX21 that have distinct biological differences in oncogenic pathways and prognosis. In the current study, we generated an immunohistochemistry (IHC) algorithm to identify the two subtypes in paraffin tissue using antibodies to key transcriptional factors (GATA3 and TBX21) and their target proteins (CCR4 and CXCR3). In a training cohort of 49 cases of PTCL-NOS with corresponding GEP data, the two subtypes identified by the IHC algorithm matched the GEP results with high sensitivity (85%) and showed a significant difference in overall survival (OS) (p=0.03). The IHC algorithm classification showed high inter-observer reproducibility among pathologists and was validated in a second PTCL-NOS cohort (n=124), where a significant difference in OS between the PTCL-GATA3 and PTCL-TBX21 subtypes was confirmed (p=0.003). In multivariate analysis, a high International Prognostic Index score (3-5) and the PTCL-GATA3 subtype identified by IHC were independent adverse predictors of OS (p= 0.0015). Additionally, the two IHC-defined subtypes were significantly associated with distinct morphological features (p<0.001), and there was a significant enrichment of an activated CD8+ cytotoxic phenotype in the PTCL-TBX21 subtype (p= 0.03). The IHC algorithm will aid in identifying the two subtypes in clinical practice, which will aid the future clinical management of patients and facilitate risk stratification in clinical trials.