1. ¹Department of Health Studies, University of Chicago, Chicago, IL, USA
2. ²Department of Surgery, University of Ibadan and University College Hospital, Ibadan, Nigeria
3. ³Department of Pathology, University of Ibadan and University College Hospital, Ibadan, Nigeria
4. ⁴Department of Radiotherapy, University of Ibadan and University College Hospital, Ibadan, Nigeria
5. ⁵Department of Medicine, University of Chicago, Chicago, IL, USA

Correspondence: Dr OI Olopade, Department of Medicine, Section of Hematology/Oncology, University of Chicago, 5841 S. Maryland Ave, MC 2115, Chicago, IL 60637, USA. E-mail: folopade@medicine.bsd.uchicago.edu

Received 5 November 2007; Revised 7 January 2008; Accepted 25 January 2008; Published online 26 February 2008.

Abstract

As the relation between reproductive factors and breast cancer risk has not been systematically studied in indigenous women of sub-Saharan Africa, we examined this in a case–control study in Nigeria. In-person interviews were conducted using structured questionnaires to collect detailed reproductive history in 819 breast cancer cases and 569 community controls between 1998 and 2006. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI). Compared with women with menarcheal age <17 years, the adjusted OR for women with menarcheal age 17 years was 0.72 (95% CI: 0.54–0.95, P=0.02). Parity was negatively associated with risk (P-trend=0.02) but age at first live birth was not significant (P=0.16). Importantly, breast cancer risk decreased by 7% for every 12 months of breastfeeding (P-trend=0.005). It is worth noting that the distribution of reproductive risk factors changed significantly from early to late birth cohorts in the direction of increasing breast cancer incidence. Our findings also highlight the heterogeneity of breast cancer aetiology across populations, and indicate the need for further studies among indigenous sub-Saharan women.