25-OH-Vitamin-D Deficiency Impairs Rituximab-Mediated Cellular Cytotoxicity and Is Associated With An Inferior Outcome Of Elderly DLBCL Patients Treated With Rituximab

To investigate the impact and underlying mechanisms of vitamin-D-deficiency (VDD) on outcome of elderly (61 to 80 year-old) DLBCL patients.

Pretreatment 25-OH-vitamin-D serum levels from 359 patients treated in the prospective multicenter RICOVER-60 trial with 6 or 8 cycles of CHOP-14 with and without 8 cycles rituximab and 63 patients in the RICOVER-noRT study treated with 6xCHOP-14 + 8xR were determined determined by LIASION®, a commercially available chemoluminescent immunoassay.

RICOVER-60 patients with VDD (defined as serum levels ≤8 ng/m l) and treated with rituximab had a 3-year event-free survival of 59% compared to 79% in patients with >8 ng/ml; 3-year overall survival was 70% and 82%, respectively. These differences were significant in a multivariable analysis adjusting for IPI risk factors with a hazard ratio of 2.1 [p=0.008] for event-free survival and 1.9 [p=0.040] for overall survival. In patients treated without rituximab 3-year EFS was not significantly different in patients with vitamin-D levels ≤8 and >8 ng/ml (HR 1.2; p=0.388). These results were confirmed in an independent validation set of 63 patients treated within the RICOVER-noRT study. Rituximab-mediated cellular toxicity (RMCC) against the CD20⁺ cell line Daudi as determined by LDH release assay increased significantly (p<0.005) in 5/5 vitamin-D-deficient individuals after vitamin-D substitution and normalization of their vitamin-D levels.

VDD is a significant risk factor for elderly DLBCL patients treated with rituximab. Our results show that VDD impairs RMCC and that RMCC can be improved by vitamin-D substitution. This together with the differential effect of VDD in patients treated with and without rituximab suggests that vitamin-D substitution might result in a better outcome of these patients when treated with CHOP plus rituximab. Supported by a grant from Deutsche Krebshilfe.

No relevant conflicts of interest to declare.