Abstract 4636: Breast cancer age-specific incidence rates among Ghanaian women by breast cancer risk factors: A study using census and population-based case-control study data
Authors: Lynn Brittny Davis , Figueroa Jonine , Biritwum Richard , Addai Beatrice Wiafe , Awuah Baffour , Clegg-Lamptey Joe Net , Adjei Robertson , Afriyie Lucy , Yarney Joel , Oti Naomi Oyoe Ohene , Ansong Daniel , Wiafe Seth , Brinton Louise , Garcia-Closas Montserrat , Graubard Barry 
Published: September 2020

Abstract
Introduction: Although breast cancer incidence in sub-Saharan African countries, including Ghana, has been historically low, incidence is rising. Evaluating age-specific incidence rates by breast cancer risk factors may provide etiologic insights. Here we present age-specific incidence rates for breast cancer estimated from the Ghana Breast Health Study (GBHS) for key breast cancer risk factors.
Methods: GBHS is a population-based case-control study with 1,071 pathologically confirmed incident invasive breast cancer cases (18-74 years old) diagnosed between 2013-2015 in three hospitals in Accra and Kumasi. A total of 2,094 controls were sampled from the population, and frequency matched by site and age to the cases. Sample weights for controls were calculated using data from the 2010 Ghana Census, adjusted for non-response. Data on incident breast cancer cases in Accra (2012-2014) and Kumasi (2013-2015) were obtained from their respective cancer registries and compared to the incidence rates observed in the GBHS. Using data from GBHS adjusted by sampling weights, we estimated 5-year age-specific breast cancer incidence rates and 95% confidence intervals overall and according to breast cancer risk factors.
Results: Age-specific breast cancer incidence rates estimated from the GBHS rose quickly until approximately age 50 when the rate plateaued but still rose (Clemmeson's hook), which was consistent with cancer registry data from Kumasi and Accra. The rates from the GBHS are not significantly different from the cancer registry rates under age 50 but are significantly higher after age 50. While the rates from the GBHS and Accra and Kumasi cancer registries were much lower than rates observed in the SEER registries for African American women, the trends were consistent. Analyses of overall rates by breast cancer risk factors showed that age-specific breast cancer risk was elevated among women with a family history of breast cancer across all ages. Data suggested cross-over interactions for other factors, particularly parity, and breastfeeding among parous women. Specifically, incidence rates were higher for parous than nulliparous women aged 20-35 years, while incidence rates were lower for parous and breastfeeding (among parous) women older than 35 years.
Conclusions: Age-specific incidence rates of breast cancer that demonstrate cross-over interactions by risk factors may be important in understanding racial disparities in breast cancer incidence, overall as well as for specific breast cancer subtypes. Elevated risk among young parous women may be indicative of the higher risk associated with early-onset (triple-negative) breast cancer.
Citation Format: Brittny Davis Lynn, Jonine Figueroa, Richard Biritwum, Beatrice Wiafe Addai, Baffour Awuah, Joe Net Clegg-Lamptey, Robertson Adjei, Lucy Afriyie, Joel Yarney, Naomi Oyoe Ohene Oti, Daniel Ansong, Seth Wiafe, Louise Brinton, Montserrat Garcia-Closas, Barry Graubard. Breast cancer age-specific incidence rates among Ghanaian women by breast cancer risk factors: A study using census and population-based case-control study data [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4636.