Efficacy of rituximab plus chemotherapy in follicular lymphoma depends on Ki-67 expression

Rituximab is widely used for the treatment of B‐cell non‐Hodgkin's lymphoma (NHL), and encouraging results have been obtained. However, some CD20‐positive NHL show minimal response to rituximab, indicating that the treatment effect depends on the presence or absence of an unidentified factor. We analyzed the relationship between the effect of rituximab plus chemotherapy and expression of Ki‐67, p53 and bcl‐2 and several clinical variables in cases of B‐NHL, particularly follicular lymphoma (FL) and diffuse large B‐cell lymphoma (DLBCL). Forty‐four patients were included in the present study, and the overall treatment response rate was 68%. Twelve of 30 patients (40%) achieved a complete response, five (16%) reached an unconfirmed complete response and 13 (43%) achieved a partial response. A high serum lactate dehydrogenase level and International Prognostic Index of high or high intermediate risk were associated with a decreased response in the case of FL. Immunohistochemical assays were performed in 18 FL patients (55%) and 15 DLBCL patients (45%). Significant correlation was found between an inferior response to treatment and high Ki‐67 expression in the cases of FL (P = 0.006). p53 and bcl‐2 expression did not correlate significantly with the response rate. The cell cycle appears to be an important factor in the efficacy of rituximab treatment. Ki‐67 expression might be a predictor of efficacy of rituximab plus chemotherapy.