BackgroundA number of epidemiological and genetic studies have attempted to determine whether levels of circulating lipids are associated with risks of various cancers, including breast cancer. However, it remains unclear if a causal relationship exists between lipids and breast cancer. If alteration of lipid levels also reduced risk of breast cancer, this could present a target for disease prevention.
DesignWe tested for an association between genetically elevated lipid levels (high-density lipoprotein cholesterol, HDL; low-density lipoprotein cholesterol, LDL; triglycerides, TG) and risk for breast cancer using Mendelian randomization (MR). Data from genome-wide association studies in 210,967 subjects from the Million Veterans Project were used to construct genetic instruments for plasma lipid traits. The effect of these instruments on breast cancer risk was evaluated using genetic data from the BCAC consortium based on 137,045 breast cancer cases and 119,078 controls.
ResultsWe observed that a 1-SD genetically determined increase in HDL levels is associated with an increased risk for all breast cancers (HDL: OR=1.08, 95% CI=1.04-1.13, P=7.4x10 -5 ). Multivariable MR analysis, which adjusted for the effects of LDL, TG, and body mass index, further improved the strength of this observation for HDL (OR=1.07, 95% CI=1.03-1.10, P=8.6x10 -5 ). We did not observe a difference in this relationship when stratified by breast tumor estrogen receptor status. We repeated this analysis using genetic variants independent of the leading association at core HDL pathway genes and found that these variants were also associated with risk for breast cancers (OR=1.11, 95% CI=1.06-1.16, P=1.5x10 -6 ), including gene-specific associations at ABCA1, APOE-APOC1-APOC4-APOC2 and CETP. In addition, we find evidence that the ABO locus is affecting both lipid levels and breast cancer.
ConclusionsGenetically elevated plasma HDL levels appear to increase breast cancer risk. Future studies are required to understand the mechanism underlying this putative causal relationship, with the goal to develop potential therapeutic strategies aimed at altering the HDL-mediated effect on breast cancer risk.