The relationship between chronic lymphocytic leukaemia and prolymphocytic leukaemia. I. Clinical and laboratory features of 300 patients and characterization of an intermediate group.

The clinical and laboratory features of 300 patients with chronic lymphocytic leukaemia (CLL) and prolymphocytic leukaemia (PLL) of B-cell type were studied in order to investigate the relationship between these two diseases. Statistical analysis demonstrated that more than 55% circulating prolymphocytes (PROL) was a defining criterion for PLL, disorder characterized by marked splenomegaly without lymph-node enlargement, cells with high density of membrane-immunoglobulin (SmIg), low mouse-rosettes (M-rosettes) and strong reactivity with the monoclonal antibody FMC7. Patients with typical CLL, defined as having less than 10% PROL, were on average 10 years younger than those with PLL and showed preferential lymph-node to spleen involvement. Characteristic markers of CLL were weak SmIg, high M-rosettes and low reactivity with FMC7. Patients with 11-55% PROL, group designated as CLL/PL, were found to have intermediate features between CLL and PLL: the degree of splenomegaly was disproportionate to the lymph-node enlargement, the number of cases with strong SmIg was closer to that found in PLL, but the other markers were not significantly different from CLL. The CLL/PL group appeared to be heterogeneous and includes at least two types of CLL, one with increased proportions of PROL but otherwise typical disease, and another in 'prolymphocytoid' transformation. Our study suggests that although PLL cannot be considered as the extreme end of a continuous spectrum from typical CLL, the spleen may be the source of PROL both in PLL and in CLL/PL.