Risk Factors for Breast Cancer, Overall and by Tumor Subtype, among Women from Mozambique, Sub-Saharan Africa

Background: Breast cancer incidence is rising in Africa, but there are scare data regarding risk factors in this region. We assessed the relation between risk factors and the occurrence of breast cancer, overall and by tumor subtype in women from Mozambique. Methods: The associations between education, number of births, height, weight, body mass index (BMI), and breast cancer risk among 138 cases (participants from the Moza-BC cohort) and 638 controls from the general population (from a World Health Organization stepwise approach to surveillance survey), recruited during 2014 to 2017, were investigated. Adjusted ORs (aOR) and 95% confidence intervals (CI) were estimated using multivariable logistic regression. Results: Multiparity (≥6 vs. 0–1 live births) was a protective factor for the development of hormone receptor (HR)–positive (aOR = 0.22; 95% CI, 0.08–0.64) and HR-positive/HER2-negative tumors (aOR = 0.20; 95% CI, 0.06–0.68), whereas a higher educational level (≥8 vs. 0 schooling years) increased breast cancer risk across all subtypes (overall aOR = 1.98; 95% CI, 1.04–3.80). Higher weight and BMI were associated with a higher breast cancer risk among postmenopausal women (per 1-kg increase: aOR = 1.05; 95% CI, 1.02–1.08; per 1-kg/m2 increase: aOR = 1.11; 95% CI, 1.04–1.18, respectively), but were protective in premenopausal women (aOR = 0.98; 95% CI, 0.96–0.99; aOR = 0.95; 95% CI, 0.91–0.99, respectively), regardless of subtype. Higher height increased the risk of HR-negative tumors in postmenopause (per 10-cm increase: aOR = 2.81; 95% CI, 1.41–6.03). Conclusion: These results demonstrate the etiological heterogeneity of breast cancer among native African women, namely regarding the differential effect of multiparity, education, and body parameters in breast cancer risk. Impact: As the prevalence of obesity grows, these findings are important to inform public health policies on cancer prevention, by highlighting obesity as a modifiable risk factor for breast cancer among African women. The Moza-BC cohort study was supported by the Beginning Investigator Grant for Catalytic Research (BIG Cat) program, an AORTIC program with support from the U.S. NCI (grant number 59-210-6-004). The WHO-STEPS Survey was funded by the Mozambican Ministry of Health and by the WHO. In addition, this study was supported by national funding from FCT – Fundação para a Ciência e a Tecnologia, I.P., under the Unidade de Investigação em Epidemiologia – Instituto de Saúde Pública da Universidade do Porto (EPIUnit; info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UIDB/04750/2020/PT). Samantha Morais was cofunded by FEDER through the Operational Programme Competitiveness and Internationalization and FCT (POCI01-0145-FEDER-032358; PTDC/SAU-EPI/32358/2017). The funders had no involvement in the analysis and interpretation of data, writing of the report, or decision to submit the article for publication. The authors thank the Calouste Gulbenkian Foundation (Portugal) and partners Camões, Institute of Cooperation and Language, Portugal; Millennium BCP Foundation, Portugal; and Millennium BIM; Mozambique, for funding the short-term training program of Assucena Guisseve at the Centro Hospitalar Universitário de São João, under the Project “Improving the diagnosis and treatment of oncological diseases in Mozambique.” The authors also thank Dr. Maria Alice Franzoi, from the Institut Jules Bordet, for her comments on the article. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.