B-Cell Prolymphocytic Leukemia (B-PLL)
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Definition
B-cell prolymphocytic leukemia is a more aggressive, but still treatable, form of chronic lymphocytic leukemia (CLL). The malignant B cells are larger than average. The name is commonly abbreviated B-PLL. It has a relatively poor prognosis.
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Epidemiology
B-PLL is an extremely rare disease, comprising approximately 1% of lymphocytic leukemias. Most patients are over 60 years of age, with the median age of 70 and a male predominance (male to female ratio 1.6 to 1)
Possible causes
Morphology
Peripheral blood and bone marrow: The majority (>55% and usually >90%) of the circulating cells are prolymphocytes - medium sized cells (twice the size of benign lymphocytes) with a round nucleus, moderately condensed nuclear chromatin, a prominent central nuceoli, and a relatively small amount of faintly basophillic cytoplasm. Some nuclear indentation may be present. The bone marrow shows diffuse intertrabecular infiltration by similar cells.
Tissue other than bone marrow: In the spleen, extensive white and red pulp involvement, with prolymphocytes present in both red and white pulp nodules. The nodules in the white pulp may show a bizonal appearance with packed cells in the center and larger cells in the periphery. Lymph nodes show diffuse and vaguely nodular infiltrates of similar cells.
Immunophenotyping
The cells of B-PLL strongly express surface light chains and IgM +/- IgD as well as B-cell antigens CD19, CD20, CD22, CD79a and CD79b, and FMC7. CD5 is only present in about 1/3 of the cases of B-PLL. CD5 is only positive in cases arising from CLL. The expression of CD20 (and surface Ig) as compared to CLL. CD23 is generally absent.
Other relevant tests
Cytochemistry
Genetics
Immunoglobulin genes are rearranged. B-PLL can involve deletions from chromosome 11 and chromosome 13. Many cases have been reported with breakpoints involving 14q32, particularly with t(11;140(q13;q320, which is found in up to 20%v of cases of PLL. Loss of heterogygosity in TP53 have been reported in 53% of cases.
Sub-classification
PLL can transform from CLL. de novo cases of PLL must be distinguished from CLL transformation, as the latter has a worse prognosis.
Flow Diagnosis
The cells in B-PLL strongly express surface Ig (kappa or lambda) and surface IgM as well as B cell markers CD19, CD20, CD22, CD79a, CD79b, FMC7. CD5 can be expressed and CD23 is generally absent.
The differential diagnosis includes splenic MZL, MCL, B-CLL and T-PLL.
References
Lens D, Matutes E, Catovsky D, Coignet LJ (2000). "Frequent deletions at 11q23 and 13q14 in B cell prolymphocytic leukemia (B-PLL)". Leukemia 14 (3): 427-30
Del Giudice I, Davis Z, Matutes E, et al (2006). "IgVH genes mutation and usage, ZAP-70 and CD38 expression provide new insights on B-cell prolymphocytic leukemia (B-PLL)". Leukemia 20 (7): 1231-7.