Abnormal patterns of antigenic expression in follicular lymphoma: a flow cytometric study.

In order to distinguish follicular lymphoma (FL) from reactive hyperplasia (RH), flow cytometric (FC) immunophenotypic studies have been used primarily to look for monotypic CD5- CD10(+) B cells with much more limited use of bcl-2 stains. We studied what additional diagnostic information could be extracted from routine FC studies in a retrospective study of 90 FL and 91 RH cases. The following significant differences were identified: dimmer CD19 on CD10+ B cells in FL (P < .0001), brighter CD10 and more numerous CD10(+) B cells in FL (P < .0001), and brighter CD20 on neoplastic B cells than on other B cells in FL (P = .002) or in RH (P = .05). In the FL cases, no correlations could be documented between any phenotypic findings. Grade 3 FL had significantly dimmer CD10 expression than lower grades (P = .05). Visual analysis of CD10(+) vs CD10(-) smaller B cells showed dimmer CD19 on the CD10(+) cells in 28 (44%) of 64 evaluable FL cases and 0 of 87 evaluable RH cases. These findings expand the ways in which FC studies can be used to help diagnose FL and suggest that the phenotypic aberrations identified do not represent normal developmental pathways.