Abstract P3-07-02: Circulating lipids and breast cancer risk – Effects of ApoB
Authors: Butt Talha , Melander Olle , Almgren Peter , Shiffman Dov , Manjer Jonas , Borgquist Signe 
Published: May 2015

Abstract
Background: Obesity in relation to breast cancer risk reveals different impact on women, warranting studies on circulating lipids and risk for breast cancer. Apolipoprotein A (ApoA), and apolipoprotein B (ApoB) are recognized actors in cardiovascular disease as the major protein components of High-Density-Lipoprotein (HDL) and Low-Density-Lipoprotein (LDL), respectively. LDL and HDL particles transport cholesterol from the liver to peripheral tissues and back. Blood levels of circulating lipoproteins and obesity are positively correlated. However the epidemiological evidence for the lipoprotein-cancer linkage has been mixed.
Aim: The aim of this study was to investigate pre-diagnostic levels of ApoA, ApoB, LDL and HDL in relation to breast cancer risk.
Methods and Material: The prospective cohort, Malmö Diet and Cancer Study was initiated in 1991 and enrolled 17035 women. These were followed-up until 31st of December 2011 and 1024 women were diagnosed with breast cancer. Blood samples were collected at baseline. Lipid quartiles (ApoA, ApoB, HDL, LDL) were constructed based on the entire female cohort, excluding women with a prevalent breast cancer. Associations between circulating lipids and patient characteristics; age at baseline, body mass index (BMI) and socioeconomic index were described with ANOVA. A multivariate Cox Proportional Hazards analyses was applied to study breast cancer risk in relation to levels of circulating lipids and a trend analysis was performed.
Results: Age at baseline was evenly distributed among quartiles of ApoA (mean 56.4 SD 8.0- 58.0 SD 7.6) and HDL (mean 57.7 SD 6.1 – 57.4 SD 5.8) For ApoB (mean 53.7 SD 7.2 - 60.3 SD 7.3 and LDL (mean 54.9 SD 5.8 – 59.5 SD 5.2), age increased with levels of lipids. BMI was negatively associated with ApoA; women in the lowest quartile had the highest BMI (kg/m2) (mean BMI in ApoA-quartiles 1-4 (26.5, 25.7, 25.0, 24.4). The same pattern was seen for quartiles of HDL whilst a reversed relationship was seen for ApoB and LDL. Socioeconomic status was evenly distributed between all measured lipid quartiles. The multivariate Cox analyses revealed a statistically significant risk reduction for women with increasing levels of ApoB. Compared with the first quartile, the risk for incident breast cancer in quartiles 2-4 was 1.01 (95%CI, 0.85-1.20); 0.82 (95%CI, 0.68-0.99); 0.73 (95%CI, 0.60-0.89), P-trend&lt;0.0003. A similar trend was seen for LDL, however only statistically significantly in the unadjusted analyses (P-trend &lt;0.016). Levels of ApoA and HDL were not significantly associated with breast cancer risk.
Conclusions: This study confirms previous studies indicating an inverse association between ApoB and breast cancer risk. Studies addressing total cholesterol have similarly shown risk-reducing effects on breast cancer risk with increasing levels of cholesterol. However, BMI does not seem to explain this association. Previous breast cancer studies on circulating lipids including all separate components, ApoA, ApoB, HDL, and LDL are sparse, and the association is still insufficiently elucidated. It is possible that ApoB and LDL as risk factors for cardiovascular events have diverse effects in breast cancer. The interaction between circulating levels of lipids and breast cancer needs to be further investigated.
Citation Format: Talha Butt, Olle Melander, Peter Almgren, Dov Shiffman, Jonas Manjer, Signe Borgquist. Circulating lipids and breast cancer risk – Effects of ApoB [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-07-02.