Significantly better prognosis for patients with primary plasma cell leukemia than for patients with secondary plasma cell leukemia.

Plasma cell leukemia (PCL) is a rare variant of multiple myeloma (MM). Patients may either present de novo (primary PCL), or PCL may occur during the course of MM (secondary PCL). We compared the laboratory and clinical findings of both primary and secondary PCL and MM to elucidate their natural history and the relationship among these entities. Ten cases of PCL (7 cases of primary PCL and 3 cases of secondary PCL) and 20 sex- and age-matched cases of MM were compared. The patients with primary PCL showed significantly lower platelet and neutrophil counts in peripheral blood and higher cellularity in bone marrow than patients with MM (p = 0.002, < 0.001 and 0.027, respectively). Immunophenotypic studies showed a different expression of HLA-DR and CD117 antigens among the 3 groups. There was a significant difference in survival between the 3 groups (median survival of primary PCL, secondary PCL and MM = 22.2, 1.3 and 36.4 months, respectively; p = 0.048). The patients with primary PCL showed better prognosis than those with secondary PCL. Primary PCL might be a differently developed disease from MM. In diagnosing PCL, it is important to differentiate primary PCL from secondary PCL for the prediction of prognosis.