Leisure-Time Physical Activity is Associated with reduced Risk of Breast Cancer and Triple Negative Breast Cancer in Nigerian Women: a matched case-control study

Background Physical activity is associated with reduced risk of breast cancer and its various subtypes but this association is less known in African women, particularly with triple-negative breast cancer that occurs more frequently in Sub-Saharan Africa compared to developed countries. In this study, we examined the association between leisure-time physical activity (LTPA) and breast cancer in total and by its subtypes in Nigerian women. Methods Overall, 630 newly diagnosed patients with primary invasive breast cancer were age-matched (±5years) with 630 controls from the Nigerian Integrative Epidemiology of Breast Cancer (NIBBLE) Study from 01/2014-07/2016. We derived the average amount of time spent on LTPA per week over the past year using a modified Nurses’ Health Study-II physical activity questionnaire. We calculated the total metabolic equivalents (METs) for each reported LTPA per hour/week (i.e. walking, cycling, and dancing) and compared odds of breast cancer among participants who attained the World Health Organization (WHO) physical activity(PA) recommendations of at least 150 minutes of moderate-intensity or/and 75 minutes of vigorous-intensity aerobic activity/week with those who did not. In addition, we evaluated this by categories of LTPA in quartiles of METs. We used conditional and unconditional logistic regression models to estimate the adjusted Odds Ratio(OR) of LTPA with overall breast cancer and by hormone receptor-positive and triple-negative breast cancer. Results The mean ages of cases and controls were similar after matching, 42.5±10.1 and 41.5±9.2 years (mean±SD), respectively. Women who attained the WHO PA recommendations had a 42% reduction in the odds of having breast cancer(OR=0.58 95% CI:0.43-0.78) compared with those who did not. LTPA was associated with reduced odds of having hormone receptor-positive by 41% and significantly associated with reduced odds of having triple-negative breast cancer by 45%. In addition, a significant dose-response relationship was observed, women with higher levels of LTPA had lower odds of having overall breast cancer as well as having triple-negative and hormone receptor-positive breast cancer. Conclusions Increasing LTPA in African women can play a significant role in reducing the incidence of breast cancer, particularly of the more aggressive subtype as triple-negative, which is more prevalent in Sub-Saharan Africa.