Abstract Higher circulating 25-hydroxyvitamin-D [25(OH)D] concentrations - used clinically to assess vitamin D status - are inversely associated with colorectal cancer (CRC) risk. However, it remains unknown whether this association varies by common, inherited polymorphisms encoding common vitamin D-binding protein (DBP) isoforms linked to differences in vitamin D handling and metabolism. We pooled participant-level data from three prospective cohorts in the United States (Cancer Prevention Study-II [CPS-II], Nurses’ Health Study [NHS]) and Western Europe (European Prospective Investigation into Cancer and Nutrition [EPIC]), comprising 1,710 incident CRC cases diagnosed between 1990 and 2011, and 1,649 matched controls selected using incidence density sampling. There were 1,106, 246 and 358 CRC cases in EPIC, CPS-II and NHS, respectively. Pre-diagnostic 25(OH)D measurements were calibrated to the same assay and seasonally-adjusted. Study-specific relative risks (RRs) for 25(OH)D and CRC risk according to DBP2 isoform (determined by the GC rs4588 variant) were estimated using multivariable unconditional logistic regression and pooled using fixed effects models. We also stratified our models by dietary vitamin D intake to account for differences in fortification/supplementation in the US and Europe. Variation in 25(OH)D concentrations across studies reflected differences in vitamin D intake and supplement use. Among individuals with lower vitamin D intakes (≤ 330 IU/day), for each 25 nmol/L increase in 25(OH)D, CRC risk was 30% lower among those with the DBP2 isoform (RR = 0.70, 95% CI = 0.59-0.83), and 5% lower among those without DBP2 (RR = 0.95, 95% CI = 0.82-1.10) (Pheterogeneity by DBP isoform = 0.009). Among individuals with higher vitamin D intakes (>330 IU/day, CPS-II and NHS only), for each 25 nmol/L increase in 25(OH)D, CRC risk was 18% higher among those with DBP2 (RR = 1.18, 95% CI = 0.82-1.10), and 33% lower among those without the DBP2 isoform (RR = 0.67, 95% CI = 0.53-0.85) (Pheterogeneity by DBP isoform = 0.002). These findings suggest that the association of 25(OH)D with CRC risk differs depending on inheritance of the functional DBP2 isoform in combination with levels of dietary vitamin D intake. <!–EndFragment–> Citation Format: David C. Gibbs, Marjorie L. McCullough, Mingyang Song, Caroline Y. Um, Kana Wu, Mazda Jenab, Edward Giovannucci, Roberd M. Bostick, Veronika Fedirko. Association of circulating vitamin D concentrations with colorectal cancer risk differs depending on inherited genotypes in combination with dietary lifestyle factors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 626.