Clonal hematopoiesis and bone marrow infiltration in patients with follicular helper T-cell lymphoma of angioimmunoblastic type

Follicular helper T-cell (TFH) lymphoma harbors recurrent mutations of RHOAG17V, IDH2R172, TET2 and DNMT3A. TET2 and DNMT3A mutations are the most frequently affected genes in clonal hematopoiesis (CH). The aim of our study was to investigate the frequency of CH in bone marrow biopsies (BMB) of TFH/angioimmunoblastic T-cell lymphoma (TFH-AITL) patients and its association with myeloid neoplasms. A total of 29 BMB from 22 patients with a diagnosis of TFH-AITL were analyzed by next-generation sequencing (NGS) with a custom panel. Morphologically, 5 BMB revealed TFH-AITL infiltrates of >5% of BM cellularity confirmed in 4 cases by NGS-based T-cell clonality. IDH2R172 was demonstrated only in 1/29 (3%), and RHOAG17V in 2/29 (7%) samples. TET2 and DNMT3A were identified in 24/29 (83%) and17/29 (59%) BMB, respectively. In the parallel lymph node (LN) the frequencies of mutations were 27% (IDH2R172), 64% (RHOAG17V), 86% (TET2), and 50% (DNMT3A). TET2 and/or DNMT3A mutations identical in LN and BMB were present in 18/22 (82%) patients, regardless of BM infiltration. In 3 cases the CH mutations were detected 13, 41, and 145 months before TFH-AITL diagnosis. Cases with TET2/DNMT3A mutations and BM variant allele frequencies (VAF) >40% (7/18, 39%) showed lower blood counts. However, only low platelet count was statistically significant (p = 0.024). Myeloid neoplasms and/or MDS-related mutations were identified in 4 cases (4/22; 18%); all with high TET2 VAFs (>40%; p = 0.0114).In conclusion, CH is present in 82% of TFH-AITL and can be demonstrated up to 145 months before TFH-AITL diagnosis. NGS T-cell clonality analysis is an excellent tool to confirm TFH-AITL BM infiltration. Concurrent myeloid neoplasms were identified in 18% of the cases and were associated with TET2 mutations with high allelic burden (>40%). We demonstrate that myeloid neoplasms might occur simultaneously or precede the diagnosis of TFH lymphoma.