Intravascular NK/T-cell lymphoma: clinicopathological and integrated molecular analysis of two cases provides a clue to disease pathogenesis.

AIMS: To elucidate the clinicopathological and molecular features of intravascular NK/T-cell lymphoma (IVNKTCL). METHODS: Two cases of IVNKTCL were retrieved from a single-centre cohort composed of 25 intravascular lymphomas. Whole-exome and RNA sequencing and immunohistochemistry were performed. RESULTS: We identified somatic mutations in the following epigenetic regulators: four histone genes (HIST1H2AN, HIST1H2BE, HIST1H2BN and H3F3A), histone deacetylase (HDAC5), two helicases (WRN and DDX3X), two methylation-related enzymes (TET2 and DNMT1) and the SNI/SWF pathway (ARID1A). Copy number analysis identified driver gene alterations comprising the loss of ARID1B, HACE1 and SMAD4, and the gain of SOX2 and histone clusters. RNA sequencing analysis did not indicate the presence of any fusion gene. Both cases were positive for Epstein-Barr virus (EBV) and showed strong expression of programmed death-ligand 1 (PD-L1). CONCLUSIONS: This study raises the possibility that, at least for some patients, IVNKTCL may be considered an epigenetic disease with EBV infection-associated aetiopathogenesis.