1549 Background: After recent advances in breast cancer treatment and increasing uptake of contralateral prophylactic mastectomies, estimates of contralateral breast cancer (CBC) risk by year of diagnosis and other patient characteristics are needed to help inform decision making. Methods: We estimated CBC risk in 399,032 1-year survivors of a first primary breast cancer (stage I-III) in the US Surveillance, Epidemiology, and End Results Database (1992-2015). CBC was defined as an invasive second breast cancer diagnosed in the opposite breast 12+ months after the first breast cancer diagnosis. We estimated standardized incidence ratios (SIRs) and 5-year cumulative incidence of CBC by calendar period, age, breast cancer subtype, and receipt of hormonal therapy for the initial breast cancer. SIRs were calculated as the observed number of CBCs among survivors compared to the expected number of first breast cancers in the general population. Cumulative incidence was estimated in women without contralateral prophylactic mastectomies and accounted for competing risks. Results: Among 399,032 breast cancer survivors, 11,365 cases of CBC were diagnosed through 2015. Risk of CBC was elevated over the entire study period (SIR = 2.23, 95% CI = 2.19-2.27). SIRs for CBC declined over calendar period and this decreasing trend was observed irrespective of age, estrogen receptor (ER) status, and hormonal therapy. Survivors had an overall 5-year cumulative incidence of CBC of 1.49% (95% CI = 1.44%-1.54%), which decreased over time to 1.31% (95% CI = 1.23%-1.41%) in 2008-2014. For recent diagnoses, the 5-year cumulative incidence of CBC was higher after ER-negative (1.80%, 95% CI = 1.55%-2.07%) and triple negative tumors (1.98%, 95% CI = 1.52%-2.55%), and lowest for women who received hormonal therapy (1.01%, 95% CI = 0.90%-1.13%). Conclusions: Although CBC risk is declining in the US from 1992-2015, survivors have approximately twice the risk of an incident breast cancer (in the contralateral breast) compared to the general population. The 5-year cumulative risk of CBC is highest after ER-negative/triple negative tumors highlighting the need for medical surveillance and targeted interventions among these patients.
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.
Background: Women of African ancestry have a higher proportion of early onset and estrogen receptor (ER) negative cancers compared to women of European descent. Differences in risk associations by age at onset and ER status for reproductive factors, particularly parity and breastfeeding, have been proposed as possible contributors to this racial disparity. We therefore investigated these relations in the Ghana Breast Health Study. Methods: The study population included 1,126 women diagnosed with invasive breast cancer and 2,106 population controls aged 18-74 years at recruitment (2013-2015) in three hospitals in Accra and Kumasi, Ghana. Factors evaluated included age at menarche, number of livebirths, age at first livebirth, and median months breastfeeding per pregnancy. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using logistic regression models overall and stratified by age. Associations by ER status were estimated using polytomous logistic regression models. Results: We observed associations with parity and extended breastfeeding duration per pregnancy that were modified by age at onset (<50 vs. >50 years, P-het <0.02 and 0.01, respectively). For women <50 years, the OR was 0.70 (95% CI 0.42-1.18) for those with >5 v. 0 livebirths, but there was no association with breastfeeding months per pregnancy (>18 vs <12 months: OR (95%CI) = 1.04 (0.75-1.44). For women >50 years, both higher number of livebirths and longer durations of breastfeeding months per pregnancy were associated with lower breast cancer risk: OR (95%CI) = 0.40 (0.20-0.83) for >5 vs 0 livebirths and 0.71 (0.51-0.98) for >18 vs <12 breastfeeding months per pregnancy. Data were consistent with a higher risk of early onset (<50 years) ER-negative breast cancer for parous compared to nulliparous women (1.63 (0.82-3.25), that was attenuated by extended breastfeeding (0.72 (0.45-1.14) for >18 vs <12 breastfeeding months per pregnancy). Conclusion: In this population of women in West Africa, increased number of live births and breastfeeding months per pregnancy were strong protective factors for later onset breast cancer. Among younger women, these trends were modified by ER status, with opposite associations for parity in ER+ vs. ER- tumors and an inverse association with breastfeeding in the ER- tumors that was not seen in the ER+ tumors. Our data support previous reports in African-American women of differential associations of parity and breastfeeding by ER status and age at onset. Further attention should focus on how reproductive factors contribute to observed racial heterogeneity in breast cancer. Citation Format: Jonine D. Figueroa, Brittny Davis Lynn, Lawrence Edusei, Nicolas Titiloye, Ernest Adjei, Joe Nat Clegg-Lamptey, Beatrice Wiafe-Addai, Baffour Awuah, Montserrat Garcia-Closas, Louise A. Brinton. Reproductive factors and breast cancer risk to women in Ghana, West Africa [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 622.
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