ABSTRACT
I. INTRODUCTION Prolymphocytic leukemia (PLL) was first described by Galton and colleagues (1974) (1) as a variant form of chronic lymphocytic leukemia (CLL). The disease is characterized by its distinct clinical and laboratory features, namely splenomegaly and high white blood cell (WBC) counts, with the circulating lymphoid cells being medium size lymphocytes with a prominent nucleolus designated “prolymphocyte.” The B-cell nature of the leuke mic cells was demonstrated in some of these cases when immunological markers first become available. Almost simultaneously, a case of T-PLL was reported in a patient with similar clinical characteristics and morphology but in whom the neoplastic circulating cells were shown to form rosettes with sheep erythrocytes (2). We have subsequently studied a large series of patients with T-PLL (3), and it has become apparent that this disease is probably as frequent as B-PLL. However, both B-and T-cell PLL are rare and only account for approximately 2% among disorders seen with >10 X 109/L lymphocyto sis. B-and T-PLL have some clinical features and cell morphology in common, and this together with historical reasons justifies retention of the term “PLL” for both diseases. However, their biology and pathogenesis are very different and, thus, they are in fact distinct clinicopathological entities.
