Comparison of CD20 expression in B‐cell lymphoma between newly diagnosed, untreated cases and those after rituximab treatment

Few studies have statistically investigated reduced CD20 expression in B‐cell lymphoma after rituximab therapy and genomic mutation of CD20 associated with reduction. We examined CD20‐positive rate in follicular lymphoma (FL) and diffuse large B‐cell lymphoma (DLBCL) by flow cytometry (FCM) and immunohistochemical staining (IHS), comparing 138 cases after rituximab therapy with 360 initial, not yet treated cases. Sequence analysis of exons 3 to 8 of CD20 was performed on 22 cases with low CD20‐positive rate after rituximab treatment. The results showed a statistical correlation between CD20‐positive rate in FCM and IHS. By FCM, the CD20‐positive rate among post‐rituximab cases was significantly lower than among initial cases in DLBCL, non‐germinal center origin B‐cell type (average values [avg] 57.8 and 87.9, respectively) (P