Subtypes of Prolymphocytic Leukemia According to Latest Classifications
The latest WHO (5th edition, 2022) and ICC (2022) classifications recognize only T-cell prolymphocytic leukemia (T-PLL) as a distinct entity, while B-cell prolymphocytic leukemia (B-PLL) has been removed as a separate diagnostic category in WHO-HAEM5. 1, 2, 3
Current Classification Status
T-Cell Prolymphocytic Leukemia (T-PLL)
- T-PLL remains a recognized distinct entity in both the 2022 WHO-HAEM5 and ICC classifications 1, 4
- First international consensus diagnostic criteria for T-PLL were recently published, refining the diagnostic approach 1
- T-PLL is characterized by complex genetic alterations with a well-characterized molecular landscape 1
B-Cell Prolymphocytic Leukemia (B-PLL)
- B-PLL is no longer recognized as a distinct entity in WHO-HAEM5 (2022), though it was included in WHO-HAEM4 (2017) 2, 5, 3
- The removal reflects substantial evidence that B-PLL represents a morphologic transformation state shared by various small B-cell lymphomas rather than a unique biologic entity 5
- Cases previously diagnosed as B-PLL show significant biologic and molecular heterogeneity, with many sharing similarities with other small B-cell lymphomas (mantle cell lymphoma, CLL with prolymphocytes, hairy cell leukemia, splenic marginal zone lymphoma) 2, 5
- De novo B-PLL cases are now considered extremely rare, and most represent prolymphocytoid transformation of other B-cell neoplasms 5, 3
Key Diagnostic Considerations
For T-PLL
- Requires bone marrow biopsy and aspirate with flow cytometry and cytogenetic studies 2
- Characterized by specific immunophenotypic and molecular features distinct from other T-cell malignancies 1
For Cases with Prolymphocytic Features
- When encountering peripheral blood with ≥55% prolymphocytes (the historical threshold for B-PLL), thorough workup is required to exclude other small B-cell lymphomas undergoing prolymphocytoid transformation 2, 5
- The diagnosis requires exclusion of mantle cell lymphoma, CLL with increased prolymphocytes, hairy cell leukemia, and splenic marginal zone lymphoma through comprehensive immunophenotyping and molecular studies 2
Clinical Implications
In summary: Only T-PLL exists as a formal subtype of prolymphocytic leukemia in current 2022 classifications. The concept of B-PLL as a distinct entity has been retired due to lack of unique biologic features and recognition that it represents a morphologic pattern rather than a discrete disease 5, 3.