Breast cancer in pre-menopausal women in West Africa: analysis of temporal trends and evaluation of risk factors associated with reproductive life.

BACKGROUND:In West Africa, trends and risk factors for breast cancer (BC) have been rarely studied. METHODS:Here we have analyzed trends of BC over two periods in two population-based cancer registries, in Mali-Bamako (1987-1997; 1998-2009) and in The Gambia (1988-1997; 1998-2006). We have conducted a case-control study (n = 253 cases, 249 controls) on risk factors associated with reproductive life stratified by menopausal status in Bamako. RESULTS:Between the two periods, BC incidence rates increased by 20% (incidence rate ratio (IRR) 1.20 (95% CI [1.07-1.35])) in Bamako, with an annual percentage change of 2% (95% CI [0.4-3.6]). The increase was of 30% in women under 55 years (IRR 1.30 (95% CI [1.14-1.60])). A similar pattern was observed in The Gambia for women under 50 years (IRR 1.47 (95% CI [1.07-2.01])). Overall, pre-menopausal breast cancer was predominant in both countries. In contrary to what is well established, case-control study showed that late age at menarche (>14 years) increased the risk of BC among pre-menopausal women (OR: 2.02 (95% CI [1.08-3.78])) while it tended to be protective in post-menopausal women (OR: 0.61 (95% CI [0.29-1.29])). Later age at a first pregnancy (>20 years) was associated with a reduction of risk in pre-menopausal women (OR: 0.41 (95% CI [0.18-0.89])). CONCLUSION:These results indicate that the burden of pre-menopausal BC is increasing in West African countries. These cancers appear to be associated with distinct reproductive risk factors, highlighting the need for better understanding the biological bases of early BC in African populations.