Immunohistochemical Subclassification of Peripheral T Cell Lymphomas-Not Otherwise Specified

Objective Peripheral T cell lymphomas-not otherwise specified (PTCL-NOS) are a heterogeneous group of mature T cell lymphomas that do not belong to any specified subtype. Gene expression profiling has revealed two biological variants of PTCL-NOS, PTCLGATA3 and PTCLTBX21. This study aims to subclassify PTCL-NOS using immunohistochemistry (IHC) and to establish its implication in prognosis. Methods A descriptive study was done using 39 morphologically and immunohistochemically diagnosed cases of PTCL diagnosed over a 10-year period, 2013 to 2022. The additional IHC markers used were GATA3 and CCR4 for PTCLGATA3 and TBX21 and CXCR3 for PTCLTBX21. All cases had a minimum follow-up of 6 months. Results After subclassification of PTCL-NOS ( n = 39), 44% were PTCLGATA3 subtype. This subtype showed monomorphic morphology and a high ki67 index, and was found to a have worse outcome. In comparison, PTCLTBX21 showed heterogeneous morphology and a low ki67 index. Conclusion Subcategorization of PTCL-NOS based on the IHC markers helps in the stratification of this disease. This will also identify cases with more aggressive behavior at the time of diagnosis.