Prognostic significance of CD38 and CD20 expression as assessed by quantitative flow cytometry in chronic lymphocytic leukaemia

CD38 expression on chronic lymphocytic leukaemia (CLL) cells is a poor prognostic factor, however, methods for measuring this vary. The QuantiBRITE(TM) flow cytometry (FC) system yields an absolute antigen expression value (antibodies bound/cell, ABC) and may be useful in standardizing CD38 expression analysis. We evaluated cryopreserved pretreatment CLL cells for CD20 ABC, CD38 ABC, and percentage of CD38(+) B cells from 131 patients requiring therapy. The 92 patients (70%) with greater than or equal to 100 CD38 ABC had worse overall survival (OS; 34% at 5 years) compared with those with < 100 CD38 ABC (70% at 5 years, mortality hazard ratio 2.30, 95% confidence interval 1.28-4.12; two-tailed P = 0.003). Among the 64 patients with < 30% CD38(+) cells, OS of the 25 with greater than or equal to 100 ABC was worse than that of the 39 with < 100 ABC (P = 0.018). OS of patients with < 30% CD38(+) cells and greater than or equal to 100 ABC was actually similar to that of patients with greater than or equal to 30% CD38(+) cells. (Bright) CD20 expression (greater than or equal to 20 000 ABC) was not associated with a worse OS (P = 0.10). The presence of greater than or equal to 100 CD38 ABC in CLL patients requiring therapy is an unfavourable prognostic factor for OS and quantitative FC may be superior to percentage CD38(+) cell assessment. Prospective trials are required to determine more precisely the prognostic significance of absolute expression levels in fresh CLL cells.