Reproductive factors and the risk of breast cancer among Nigerian women

Available estimates suggest that breast cancer incidence in Nigeria rose from 24.7/100,00 women/year in 1999 to 49/100,000 women/year in 2020. Its current mortality rate (25.5/100,000/year) ranks highest in Africa.  

Although changes in reproductive behaviours similar to the observations in high income countries have been implicated, their roles have not been widely investigated in sub-Saharan Africa. The aim of this study was to investigate the relationship between breastfeeding, age at first birth, age at last birth and the risk of breast cancer among Nigerian women. The study was a multisite hospital-based case-control design involving 379 histologically confirmed breast cancer cases and 403 controls. 

The participants aged 20 years and above were interviewed in-person between October 2016 and May 2017 using a pretested questionnaire. Cases were selected from oncology wards and controls from ophthalmology wards. Breastfeeding history, lifetime duration of breastfeeding, age at first birth, and age at last birth were self-reported. Data from all women, older women(>50years) and younger women (<50 years) were analysed using multivariable logistic regression based on Statistical Software for Social Sciences, adjusting for relevant confounders. Following confounder adjustments, women who had ever breastfed had a reduced risk of breast cancer compared to women who had never breastfed

Every additional 6 months of breastfeeding over a lifetime reduced breast cancer odds by: 7% (95% CI: 1%, 12%) in all women, 15% (95% CI: 5%, 24%) in women<50 years. Age at last birth ≥ 36 years increased breast cancer risk (OR 2.53, 95% (1.41, 4.53, p for trend =0.007) compared to age at last birth < 32 years. Age at first birth was significantly associated with an increased risk of breast cancer among women with oestrogen receptor positive breast cancer only (OR 1.09, 95% CI: 1.02, 1.17, p for trend=0.017). While advanced ages at first and last births have potential to increase breast cancer risk, longer duration of breastfeeding can reduce breast cancer risk. Improved breastfeeding practices, family planning decisions that encourages timely completion of birth should be promoted in Nigeria and other sub-Saharan African countries.