Prognostic impact of six versus eight cycles of standard regimen in patients with diffuse large B-cell lymphoma: propensity score-matching analysis

R-CHOP-21 has been the standard treatment for diffuse large B-cell lymphoma (DLBCL), but there is a paucity of evidence focusing on the number of cycles of regimens. We conducted a retrospective study to compare the effectiveness of six cycles of standard regimens versus eight cycles for overall survival (OS) in DLBCL patients using propensity score matching, in consideration of relative dose intensity (RDI). A total of 685 patients with newly diagnosed DLBCL were identified in three institutions from 2007 to 2017. Patients treated using six cycles of standard regimens were matched by propensity scores with those treated using eight cycles. A 1 : 1 propensity score matching yielded 138 patient pairs. Eight cycles did not significantly improve OS in the conventional Cox proportional hazards model (hazard ratio 0.849, 95% confidence interval 0.453-1.588, P = 0.608). Restricted cubic spline Cox models for OS confirmed that the effect of the number of cycles was not modified by total average RDI, the International Prognostic Index, and age. Occurrence of adverse events did not differ between six and eight cycles. Even considering the impact of RDI, six cycles of the initial standard regimen for DLBCL is not inferior to eight cycles. •The optimal number of cycles of standard regimens including R-CHOP-21 for newly diagnosed DLBCL has not been determined.•This study was conducted to verify whether six cycles or eight cycles of standard regimen improved the prognosis of DLBCL.•Propensity score matching and a Cox hazards model with restricted cubic spline were used in this study.•No survival benefit of eight cycles compared with six cycles was seen, even taking into account RDI.•Prognosis was no better with eight cycles of (R-)CHOP-21 or THP-COP-21 than with six cycles, after age and IPI modifications.