Prolymphocytoid variants of chronic lymphocytic leukaemia: an immunological and morphological survey

Of 417 cases of chronic lymphocytic leukaemia (CLL) examined morphologically, 346 (83%) showed low (less than 10%) numbers of cells with prolymphocytoid (PLC) morphology. Immunological studies in 267 of these cases, with particular reference to membrane surface immunoglobulin (SIg) densities and FMC7 expression, revealed that of 223 cases with insignificant prolymphocytoid components, 185 were phenotypically consistent with typical CLL whilst the other 38 cases showed significant (greater than 20% positive cells) FMC7 expression and/or increased SIg density. In contrast, 40 of the 44 cases with greater than 10% PLC showed atypical immunophenotypic features even though the expression of individual membrane components associated with B-cell differentiation appeared to be unrelated. MRBC receptor expression showed little correlation with the degree of prolymphocytoid change although all TU1- cases showed greater than 10% PLC. The results suggest that abnormal phenotypic features, similar to those observed in "prolymphocytoid" transformation, may be found in cases of CLL in the absence of morphological change.