CLL/prolymphocytic leukemia (CLL/PLL) and B-prolymphocytic leukemia (PLL) are disorders that are distinguished from CLL and from each other based on morphological determination of the percentage of prolymphocytes (large lymphoid cells with ample cytoplasm and nuclei with prominent central nucleoli). PLL is usually a de novo process without a prodromic chronic phase. CLL/PLL is arbitrarily defined as CLL demonstrating between 10 and 55% prolymphocytes, and PLL is defined as more than 55% prolymphocytes. Consequently, PLL exhibits a more morphologically monomorphous population of cells than those of CLL/PLL, which are uniformly larger than the lymphocytes seen in CLL.
The prolymphocytic component in CLL/PLL or PLL has a highly variable phenotype, reflecting the vague definition of CLL/PLL or PLL. PLL is described as CD5-, CD10-, CD23-, CD19+, and intense expression of CD20, CD22 and sIg compared with CLL (30). However, prolymphocytes may demonstrate expression of CD5, which adds difficulty in clearly delineating PLL from CLL.
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