Chronic lymphocytic leukaemia CD20 expression is dependent on the genetic subtype: a study of quantitative flow cytometry and fluorescent in-situ hybridization in 510 patients

CD20 is an important therapeutic target in chronic lymphocytic leukaemia (CLL). In order to examine the relationship between CD20 expression and cytogenetic abnormalities, we correlated the fluorescent in-situ hybridization (FISH) genetic subtype of 510 treatment-naïve patients with CD20 expression as measured by quantitative flow cytometry. Patients were classified using the Dohner hierarchial classification. The median numbers of CD20 antigen sites by FISH subtypes were: 17p- ( n  = 26), 9341 per cell; 11q- ( n  = 42), 5886 per cell; +12 ( n  = 93), 23 603 per cell; negative FISH ( n  = 153), 8828 per cell; and 13q- ( n  = 196), 10 781 per cell. Compared to cases with negative FISH, 11q- cases had significantly lower CD20 expression ( P  = 0·001), and +12 cases had significantly higher CD20 expression ( P  < 0·001). The significance of trisomy 12 and high CD20 expression was maintained after multivariate analysis accounting for other disease characteristics. Fifty-nine patients received the combination of rituximab and granulocyte-macrophage colony-stimulating factor as frontline therapy; responses were observed in 13 of 14 (93%) patients with +12, in two of four (50%) patients with 11q-, and in 30 of 41 (73%) patients with negative FISH, 13q- or 17p- CLL. Leukemic CD20 expression differed significantly between FISH subtypes. Patients with trisomy 12 CLL showed strong leukemic cell CD20 expression and had a high rate of response to rituximab-based therapy.