Understanding splenic B‐cell lymphoma/leukaemia with prominent nucleoli: Diagnosis, underpinnings for disease classification and future directions

The 5th edition of the WHO classification of haematolymphoid tumours (WHO-HAEM5) introduced a new category, splenic B-cell lymphoma/leukaemia with prominent nucleoli (SBLPN). The diagnostic entity B-cell prolymphocytic leukaemia (B-PLL) has been discontinued and the category of hairy cell leukaemia variant (HCLv) has been conceptually reframed. B-PLL and HCLv diagnoses were uncommon. Overlap existed between B-PLL and other indolent lymphomas like chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL). HCLv lacked consistent cytomorphological, immunophenotypic and genetic features. To address these issues, the WHO-HAEM5 classification has introduced SBLPN to serve as a temporary holding ground for entities that do not neatly fit into the existing classification. Cases previously classified as CD5-negative B-PLL and HCLv fall under the SBLPN category. Some splenic marginal zone lymphoma and splenic diffuse red pulp small B-cell lymphoma cases with higher number of medium or large nucleolated B cells would also be classified as SBLPN under the WHO-HAEM5. This review explores the rationale for discontinuing B-PLL and HCLv diagnoses. It then examines the concept of SBLPN, offers practical guidance for diagnosis and discusses future directions in classifying splenic B-cell lymphomas.