Prolymphocyte Leukemia

Prolymphocytic leukemia (PLL), once thought to be a variant of CLL,198 is now a well-characterized clinicopathological entity characterized by specific morphological, immunophenotypic, and histological criteria.199,200 The relative frequency of PLL among patients with chronic lymphoproliferative disorders at one large center was 10 percent compared with 80 percent for CLL and 10 percent for hairy cell leukemia.201 B-cell PLL accounts for approximately 80 percent of cases with the more aggressive T-cell PLL accounting for the remainder. PLL is clinically distinct from CLL on the basis of prominent splenomegaly, minimal adenopathy, and extreme leukocytosis with about 50 percent of patients displaying thrombocytopenia, consistent with advanced stage disease (Plate 3-2G,H).

The prolymphocyte is larger than the typical mature lymphocyte of CLL, contains more cytoplasm, and has a prominent nucleolus; however, in contrast to a lymphoblast, nuclear chromatin is relatively condensed (Plate 3-2I). Ultrastructural features include scarce polyribosomes and lysosomes, poorly developed Golgi apparatus, and short segments of rough endoplasmic reticulum.200 Morphologic variants such as cells with nuclear clefting and intermediate forms with a size between PLL cells and CLL cells may account for up to 20 percent of the WBC differential.199 Patients with between 10 and 55 percent circulating prolymphocytes have intermediate features between CLL and PLL.202 PLL may be immunopheno-typically distinguished from CLL due to a more intense staining for surface IgM and IgD and inability to form rosettes with mouse blood cells.201 Importantly, the CD5 antigen, characteristic of CLL cells, is not expressed on PLL cells. The alpha-naphthyl acetate esterase (ANAE; nonspecific esterase) stain is strongly positive in T-cell PLL; the acid phosphatase reaction tends to be stronger in T-cell PLL then in B-cell PLL.199,203

Table 3-6. Features of Hairy-Cell Leukemia and Similar Disorders

Chronic

Hairy-Cell Lymphocytic Leukemia Leukemia

B-Cell

Promyelocyte Leukemia

Splenic Lymphoma with Villous Lymphocytes

Hairy-Cell Leukemia Variant

M:F ratio

4:1

1.5:1

1.5:1

2:1

4:1

Palpable splenomegaly

75-90%

>50%

>90%

80%

>90%

Palpable lymphadenopathy

5%

70%

30%

25%

<5%

Pattern of marrow involvement

Patchy or

Nodular and/or

Nodular and/or

Nodular, or

Patchy or

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