A case-control study of 10,757 individuals to assess potentially modifiable risk factors, including stress, for breast cancer among Chinese patients in Hong Kong.

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e22522 Background: Breast cancer is the most common cancer in women worldwide. Both intrinsic and environmental factors contribute to the disparities in breast cancer incidence across different regions. In Hong Kong, the incidence has been increasing in the past decades. With over 4700 women diagnosed in 2019, breast cancer is responsible for 27% of all female cancers in Hong Kong. Apart from intrinsic non-modifiable risk factors, some risk factors are modifiable and may reduce cancer risk. Methods: We conducted a case-control study that involved breast cancer patients from the Hong Kong Breast Cancer Registry with matched healthy controls from the community between 2014 and 2017. A standardized written questionnaire was used through face-to-face interviews of all study participants. The questionnaire collected information on participants’ demographics, general health, smoking history and other lifestyle factors including physical activity, self-assessed dietary habits (balanced, vegetarian, meat and dairy-rich diets), self-perceived stress levels (measured with a 4-point Likert scale, and high stress level was defined as having over 50% of the participant’s time with stress being scored 3 or above out of a Likert scale of 4), body mass index, family history, menstrual and reproductive history, and history on the use of oral contraceptives and hormone replacement therapy. Multiple logistic regression was fitted to compare all risk factors. Results: A total of 5,186 breast cancer patients and 5,571 controls were recruited. Modifiable risk factors that were shown to be associated with an increased risk of breast cancer included self-perceived high stress level (adjusted odd ratios [aOR] = 3.44; 95% CI = 3.13-3.78), meat-rich diet (aOR = 1.77; 95% CI = 1.54-2.04), dairy-rich diet (aOR = 3.33; 95% CI = 2.01-5.52), overweight/obese status (aOR = 1.21; 95% CI = 1.10-1.32), delayed child-bearing (aOR = 2.23; 95% CI = 1.79-2.79), nulliparity (aOR = 1.21; 95% CI = 1.08-1.35) and ever use of oral contraceptives (aOR = 1.34; 95% CI = 1.22-1.47), while exercise (OR = 0.62; 95% CI = 0.56-0.68) and breast-feeding (aOR = 0.76; 95% CI = 0.69-0.83) were associated with reduced risk. Conclusions: In Hong Kong, high stress level, meat- and dairy- rich diet, overweight/obese, reproductive history and use of oral contraceptives were identified to be modifiable risk factors for breast cancer. Adjusting these factors through lifestyle modification may curb the increasing trend of breast cancer incidences in the coming decades.