Implementation of the recommended immunohistochemistry algorithm for classification of peripheral T‐cell lymphoma, not otherwise specified into the prognostically significant GATA3 and TBX21 subtypes

Introduction Current molecular research has shown the several oncogenic pathways that give rise to the peripheral T‐cell lymphoma, not otherwise defined (PTCL, NOS) subtypes, which alter prognosis and might have predictive value. This study was conducted to assess the immunohistochemistry (IHC) algorithm by Amador et al for the subtyping of PTCL, NOS and determine its applicability in relation to the clinicopathological profile. Methods This study included 43 patients with PTCL, NOS diagnosis. Following the use of IHC for the transcription factors GATA3, TBX21, CCR4, and CXCR3, two pathologists subtyped the samples. Comprehensive clinicopathological correlation was carried out. Results Applying the algorithm of Amador et al., cases were classified into GATA3 (20), TBX21 (15), and unclassified (8) subtypes. No significant association with clinical parameters of subtypes or CD4/ CD8 positivity was observed. Although a higher proportion of cases in the TBX21 subgroup showed a polymorphic population compared with the GATA3 subgroup, which had a monomorphic population, no significant p‐value (0.111) was observed. Two Lennert lymphomas were classified into the GATA3 subgroup. Multivariate analysis showed no significant difference in overall survival (p‐value = 0.105) and progression‐free survival (p‐value = 0.0509) between IHC‐defined subtypes; trends indicate that overall survival and progression‐free survival are worse in the GATA3 subgroup. Conclusion Although the algorithm is reproducible, a proportion of cases remains unclassifiable and may require additional investigation and gene expression profiling. The GATA3 subgroup was found to have a monomorphic population with a poor overall prognosis and thus requires a larger sample size for validation.