Splenic diffuse red pulp small-B cell lymphoma: toward the emergence of a new lymphoma entity.

Among splenic lymphomas with circulating cells presenting cytoplasmic projections, a homogeneous clinico-pathological entity has been recently individualized as Splenic Diffuse Red Pulp Lymphomas (SDRPL) and introduced in the provisional "unclassifiable splenic lymphoma" category of the current updated WHO classification until more is known. SDRPL presents characteristic circulating basophilic villous lymphocytes and diffuse infiltration of the splenic red pulp, distinct from Splenic Marginal Zone Lymphoma (SMZL) and Hairy Cell Leukemia (HCL), but reminiscent of HCL-Variant (HCL-V). Series of SDRPL remain sparse in the literature and controversies exist about the relationship with other splenic lymphomas. Distinction of these disorders at diagnosis can be difficult, but an adequate diagnosis is important due to differences in patient management and clinical outcome. Especially, BRAF mutations have been detected in almost all patients with HCL that may have implications for pathogenesis, diagnosis, and targeted therapy. This review will report literature data and discuss the differential diagnosis, particularly with HCL-V.