8569 Background: Vitamin D deficiency was shown to be is associated with a worse outcome in patients with non-Hodgkin's lymphoma (Drake et al., 2010) To study whether this observation could be confirmed in patients with aggressive B-cell lymphomas treated uniformly within a prospective trial, we analyzed 25-OH vitamin D serum levels in patients treated within the RICOVER-60 trial of the DSHNHL. Methods: 25-OH Vitamin D serum levels were determined with a commercial chemoluminescence immunoassay in the serum from elderly patients of the RICOVER-60 trial which compared 6 or 8 cycles of CHOP, both with and without rituximab. Results: 193 of 359 pts (53.8%) had vitamin D deficiency (<10 ng/ml) and 165/359 patients (46.0%) had vitamin D insufficiency (10-30 ng/ml) according to current definitions. When treated with R-CHOP, patients with vitamin D levels ≤8 ng/ml had a 3-year EFS of 59% compared to 79% of patients with vitamin D serum levels >8 ng/ml; the respective figures for 3-year overall survival were 70% and 82%, respectively. In R-CHOP pts these differences were significant in a multivariable analysis adjusting for IPI risk factors with a hazard ratio (HR) of 2.1 (p=0.008) for EFS and a HR of 1.9 (p=0.040) for OS. In pts treated without R effects of vitamin D deficiency were significant only for OS (HR 1.8; p=0.025), but not with respect to EFS (HR 1.2; p=0.388). These results were confirmed in an independent validation set of 63 patients treated within the prospective RICOVER-noRx study. Conclusions: Vitamin D deficiency is a significant risk factor for patients with aggressive B-cell lymphomas treated with R-CHOP. The stronger adverse effect of vitamin D deficiency in patients receiving rituximab suggests that vitamin D deficiency interferes with the R mechanisms of this antibody. A prospective study evaluating the effects of vitamin D substitution on outcome of patients receiving R-CHOP is warranted. Supported by Deutsche Krebshilfe.