BRAF V600E-positive monomorphic epitheliotropic intestinal T-cell lymphoma complicating the course of hairy cell leukemia

Abstract Hairy cell leukemia (HCL) is an uncommon B-cell chronic lymphoproliferative disorder whose pathogenesis and recurrence are strictly dependent on the presence of the BRAF V600E mutant. A 65-year-old male presented a monomorphic epitheliotropic intestinal T-cell lymphoma (formerly enteropathy-associated T-cell lymphoma, type II) with HCL not responding to first-line induction with cladribine. The intestinal lymphoma bears the BRAF V600E mutant, which is the molecular hallmark of HCL, being implicated in its pathogenesis. The case is of interest, as it provides the first description of a BRAF V600E-positive intestinal T-cell lymphoma, along with immunohistochemical and molecular demonstration, occurring in concomitance with HCL. A novel digital PCR-base method for HCL disease assessment is also suggested.