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

Summary 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.