Breast cancer risk after full-term pregnancies among African women from Nigeria, Cameroon, and Uganda

BACKGROUND The breast cancer (BC) risk profiles of African women differ significantly from those of women of European ancestry. African women are younger at the age of onset and tend to have high parity. The purpose of this study was to examine the relationship between full-term pregnancy (FTP) and the risk of BC. METHODS A case-control study was conducted among 1995 women with invasive BC and 2631 controls in Nigeria, Cameroon, and Uganda. Odds ratios (ORs) for individual ages at FTP according to the time since delivery were calculated and adjusted for confounders. A fitted spline model was used to assess the impact of the number of pregnancies on BC risk. RESULTS In comparison with a nulliparous woman, a parous woman with her first FTP at 20 years showed an OR of 0.76 (95% confidence interval [CI], 0.57-0.99) for developing BC in the following 5 years. Ten years later, this risk was 0.76 (95% CI, 0.58-0.99) and 0.76 (95% CI, 0.58-0.98) for women aged 25 and 30 years, respectively. Similarly, a parous woman with 1 pregnancy had an OR of 0.69 (95% CI, 0.49-0.96), whereas the OR was 0.66 (95% CI, 0.48-0.91) with 2 or 5 pregnancies and 0.67 (95% CI, 0.47-0.94) with 6 pregnancies in comparison with nulliparous women. CONCLUSIONS In contrast to studies in women of European ancestry, this study showed no transient increase in the risk of developing BC after FTP among African women. Further studies are needed to examine the impact of reproductive factors on early-onset BC in African women. Cancer 2015;121:2237-2243.