B-Cell Prolymphocytic Leukemia

CLINICAL FEATURES

• De novo chronic B-cell leukemia, > 55% circulating peripheral blood prolymphocytes

• Exclude transformed CLL or preexisting CLL with increased prolymphocytes

• Relatively rare tumor, accounting for <1% or less of lymphoid leukemias

• Males slightly more commonly than females

• Median age, 65 - 70 years

• Presentations:

  • Marked leukocytosis, frequently >100 × 10⁹/L, with absolute lymphocytosis

  • Splenomegaly, often anemia and thrombocytopenia

  • No or minimal lymphadenopathy

PERIPHERAL BLOOD FINDINGS

• Prolymphocytes

  • Cell size: medium, minimal cell-to-cell variability

  • Nucleus: round without significant nuclear membrane irregularity, moderately condensed chromatin (not finely dispersed), a single prominent nucleolus

  • Cytoplasm: minimally to moderately abundant, well-defined borders

BONE MARROW FINDINGS

• Typically show extensive diffuse or interstitial involvement of the marrow space

• May have a focal nodular, nonparatrabecular pattern

• Tumor cells relatively uniform, small to medium size, prominent small central nucleolus and a rim of amphophilic cytoplasm

SPLEEN FINDINGS

• Involvement of both red and white pulp regions, with expansion of red pulp sinusoids and white pulp

IMMUNOPHENOTYPE

• Positive: CD19, CD20, CD22, CD79a, FMC7

• Monotypic surface light-chain immunoglobulin

• Aberrant CD5 antigen expression in <50% of cases

• CD23 negative

CYTOGENETICS AND GENETICS

• 17p-, deletion of TP53 gene, 50%
• Lack of t(11;14)(q13;q32)

DIFFERENTIAL DIAGNOSES

• CLL in prolymphocytic transformation: presence of a substantial population of typical CLL cells, prolymphocytes < 55%

• Large B-cell lymphoma involving peripheral blood: rarely associated with a marked lymphocytosis, tumor cells much larger and more pleomorphic

• T-cell prolymphocytic leukemia: often with bulky lymphadenopathy, CD4+, TCL1+

• Mantle cell lymphoma: t(11;14), BCL1+
• SMZL
  • Clinically, SMZL associated with relatively indolent behavior
  • Peripheral blood: variable cytologic features with PLL-like cells, plasmacytoid cells, and “villous” cells
  • Bone marrow: nodular aggregates of monocytoid cells or a subtle intrasinusoidal infiltration, in contrast to the more leukemic interstitial pattern of B-PLL
• HCLv
  • Currently included in "splenic B-cell lymphoma/leukemia, unclassifiable"
  • Marked splenomegaly and high peripheral white blood cell counts
  • Cytologically, HCLv cells show some similarity to B-PLL cells with a single prominent nucleolus. HCLv cells retain delicate fibrillary cytoplasmic membrane borders and may have a sponge-like chromatin pattern similar to that of typical HCL or a more unusual blastoid or convoluted nuclear cytology.
  • HCLv shows a pure red pulp pattern in the spleen and an interstitial or sometimes diffuse pattern in the bone marrow
  • CD103+,  and bright CD11c and CD22