Vitamin D binding protein genetic isoforms, serum vitamin D, and cancer risk in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial

by Stephanie J. Weinstein, Dominick Parisi, Alison M. Mondul, Tracy M. Layne, Jiaqi Huang, Rachael Z. Stolzenberg-Solomon, Regina G. Ziegler, Mark P. Purdue, Wen-Yi Huang, Christian C. Abnet, Neal D. Freedman, Kai Yu, Demetrius Albanes

Associations between vitamin D biochemical status and cancer may be modified by vitamin D binding protein isoforms which are encoded by GC (group-specific component). We examined interactions between serum 25-hydroxyvitamin D [25(OH)D], the Gc isoforms Gc1-1, Gc1-2, and Gc2-2, and cancer risk within the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial cohort based on 3,795 cases and 3,856 controls. Multivariable-adjusted logistic regression models estimated odds ratios (ORs) and 95% confidence intervals (CIs) of cancer risk according to 25(OH)D quantiles, stratified by Gc isoform. Separately, the GC-cancer risk association was examined using proportional hazards regression among 109,746 individuals with genetic data and 26,713 diagnosed with cancer. Specific vitamin D binding protein isoform subtypes were delineated and analyzed, including Gc1-1 subtypes (Gc1s-Gc1s, Gc1f-Gc1s, and Gc1f-Gc1f) and Gc2 subtypes (Gc1s-Gc2, Gc1f-Gc2, and Gc2-Gc2). For most cancers, the GC genotype did not modify the risk associations for 25(OH)D; e.g., the OR for high vs. low vitamin D quintile was 1.09 (0.89–1.33) for overall cancer risk among individuals with the Gc1-1 isoform and 1.04 (0.83–1.31) among those with either the Gc1-2 or Gc2-2 isoforms. ORs for high compared to low vitamin D tertile for colorectal, lung, breast, and prostate cancer among those with the Gc1-1 vs. any Gc2 isoforms were, respectively, 0.60 vs. 0.73, 1.96 vs. 1.03, 1.30 vs. 1.18, and 1.19 vs. 1.22 (all p-interaction ≥0.36). However, GC qualitatively modified the vitamin D-bladder cancer risk association: OR = 1.70 (95% CI 0.96–2.98) among those with the Gc1-1 isoform and 0.52 (0.28–0.96) among those with any Gc2 isoforms (p-interaction = 0.03). When modeled without regard for 25(OH)D, Gc isoforms were generally not associated with cancer risk, although melanoma risk was significantly lower among individuals with the “f” subtype of the Gc1-1 isoform, specifically HR = 0.83 (95% CI 0.70–0.98) for Gc1f-1s and 0.67 (0.45–1.00) for Gc1f-1f, compared to individuals with the Gc1s-Gc1s isoform. Vitamin D binding protein genetic isoforms may be associated with melanoma risk but do not modify the association between vitamin D status and cancer, with the possible exception of bladder cancer.