Characterization of incidentally identified minute clonal B-lymphocyte populations in peripheral blood and bone marrow.

We describe 69 patients in whom small clonal B-cell populations were detected incidentally in blood and bone marrow samples by flow cytometric studies. In 20 patients (29%), non-Hodgkin lymphoma (NHL) subsequently was diagnosed 0 to 40 months (median, 0.1 month) from initial flow cytometric studies. In 49 patients (71%), there was no evidence of NHL after 0.5 to 72 months (median, 16 months). Patients without overt NHL had a higher absolute WBC count than patients with NHL (2,260/microL vs 1,470/microL [2.26 vs 1.47 x 10(9)/L]; P < .01). Otherwise, there were no clinical or hematologic differences between the 2 groups. We identified 70 clonal populations in the 69 patients, ranging from 0.05% to 4.5% (median, 1.28%) of events. The mean percentage of clonal B cells was similar for the 2 groups. The populations were CD5-/CD10- in 34 cases; CD5+, chronic lymphocytic leukemia-like in 19; CD5+, indeterminate in 9; CD10+ in 3; hairy cell leukemia-like in 3; and CD5+, mantle cell lymphoma-like in 2. There were no immunophenotypic differences in patients with and without overt NHL.