Comprehensive comparison of international prognostic indexes for follicular helper T-cell lymphoma

In 2016, World Health Organization classification of lymphoid neoplasms separated firmly-follicular helper (Tfh) cell origin lymphomas from peripheral T-cell lymphoma-not specified (PTCL-NOS) based on their unique immunogenic characteristics. Generally, Tfh cell origin lymphoma, which has an approximately 25% incidence, is classified into three categories: angioimmunoblastic T-cell lymphoma (AITL), follicular peripheral T-cell lymphoma (F-PTCL), and nodal peripheral T-cell lymphoma with a T-follicular helper phenotype (nodal PTCL with Tfh cell phenotype). Their prognosis has been estimated using four traditional prognostic tools for T-cell lymphoid malignancies: the international prognostic index (IPI), the prognostic index for peripheral T-cell lymphoma unspecified (PIT), the modified PIT (mPIT) and the international T-cell lymphoma project index. In addition, the AITL score that reflects AITL characteristics well has been introduced recently. However, there are no clear guidelines for evaluating the prognosis of Tfh cell lymphoma. Thus, we performed a comparative analysis to determine which of these five indexes is most suitable for Tfh cell lymphoma. We evaluated the accuracy of classification according to risk score and predicted survival rate. Based on review by lymphoma pathology experts, we enrolled 198 patients diagnosed with Tfh cell lymphoma in this retrospective study. AITL was the most common subtype (n = 168), followed by F-PTCL (n = 21) and nodal PTCL with Tfh cell phenotype (n = 9). The median progression-free survival and overall survival with front-line treatment was 0.8 years (95% confidence interval [CI], 0.6-1.1 years) and 2.9 years (95% CI, 1.6-4.2 years), respectively. The AITL score showed better differentiation than other scoring systems in terms of classification according to risk score. However, for predicting PFS (concordance-index [C-index], IPI vs. PIT vs. modified PIT vs. international T-cell lymphoma project index vs. AITL score; 0.617 vs. 0.605 vs. 0.576 vs. 0.591 vs. 0.592) and OS (C-index, IPI vs. PIT vs. modified PIT vs. international T-cell lymphoma project index vs. AITL score; 0.663 vs. 0.651 vs. 0.612 vs. 0.672 vs. 0.583), the IPI, and the international T-cell lymphoma project index showed better performance. In conclusion, there are unmet needs to develop a prognostic index for Tfh cell lymphoma because its characteristics differ from PTCL-NOS. Although the AITL score reflects Tfh cell-origin lymphoma characteristics well and clearly shows their power of classification according to risk score, there are concerns about accurate prediction of survival outcomes. Therefore, it seems too early to settle on a single scoring system in Tfh cell origin lymphoma. In the future, along with classification, a more effective tool for survival prediction needs to be developed that reflects the specific characteristics of T-cell lymphoma.