Incident breast cancer burden attributable to modifiable risk factors among Hong Kong Chinese women population (abstract)

Abstract

Background: Globally breast cancer is the most common malignancy in women, accounting for an estimated one-quarter of all female malignancies. Hong Kong (HK), a westernized and urbanized Chinese city, suffers heavy health and economic burdens from breast cancer, and the city does not have population-based screening for breast cancer. In this study, we aim to provide systematic assessment on the current breast cancer disease burden attributable to known modifiable risk factors, and to evaluate the potential effects of risk factor modifications for HK Chinese women. The findings would be useful for developing population-specific risk reduction strategies for cancer control. Methods: We estimated the population attributable risks PAR of three selected known modifiable risk factors such as lifestyle modification (obesity, physical inactivity) and reproductive history (parity) for HK Chinese women population. We applied Bruzzi et al. methods that allow for the joint PAR estimation for combinations of risk factors/exposures. We included the following variables in our analyses: excess weight in terms of BMI>=23, physical inactivity, and age at first live birth. We obtained data from the on-going population-based case control study, namely Hong Kong Breast Cancer Study (HKBCS), where data collection commenced in September 2016 and is expected to finish in 2019. In the PAR estimation, we used distribution of exposures and the relevant risk ratios estimated from HKBCS. We applied multivariable logistic regression methods to estimate the relevant risk ratios. The 95% confidence intervals were estimated using bootstrapping method. The PAR estimates were further analyzed and stratified by menopausal status. Counterfactual scenarios of exposures were studied. Results: We included 3522 cases (women with invasive breast cancer or ductal carcinoma in situ) and 2653 controls (women without breast cancer) from HKBCS (n=6175) with the recruitment period between September 2016 and September 2018. The estimates will be updated when HKBCS is concluded. Overall, appropriate control of the modifiable lifestyle (obesity, physical inactivity) and reproductive factors (parity) could reduce breast cancer incidences and its related burdens by 16.1% (95%CI = 8.6, 22.8) for HK Chinese women. The risk factors such as obesity and physical inactivity that are modifiable at menopause account for 7% of postmenopausal breast cancer. The largest individual PAR% was 13.3% (95% CI = 8.7, 17.6), for age at first live birth. Other individual PAR%s were modest. Discussion: A moderate proportion of breast cancer amongst HK women is preventable. Whilst our PAR% estimates are somewhat lower than those for US and UK women (with the age at first live birth being the exception), our findings are important for health policy makers concerned with preventive measures and public health intervention establishment for cancer control.