ASPO Abstracts

Authors: Ramin C., Mullooly M., Schonfeld SJ., Advani, PG., Bodelon C., Gierach GL., Berrington de Gonzalez A.

Category: Survivorship & Health Outcomes/Comparative Effectiveness Research
Conference Year: 2020

Abstract Body:
Purpose of the study: Approximately 5% of breast cancer survivors, aged 50 years or older, will develop a contralateral breast cancer (CBC) within 10 years after a breast cancer diagnosis. It is unknown whether pre- diagnostic lifestyle and reproductive factors, and to what extent clinical characteristics of the first breast cancer, are associated with the development of CBC in older postmenopausal women. Methods: We identified 11,267 postmenopausal women diagnosed with a first primary breast cancer (81% invasive; mean age=69 years) between 1995-2011 in the NIH-AARP Diet and Health Study. CBC was defined as a second primary breast cancer diagnosed in the opposite (contralateral) breast at least 3 months after the first breast cancer diagnosis. Exposures included pre-diagnostic lifestyle (body mass index, physical activity, smoking status, alcohol consumption) and reproductive factors (age at menarche, reproductive behavior, menopausal hormone use, age at menopause), and clinical characteristics of the first breast cancer (age at diagnosis, year of diagnosis, stage, grade, hormone receptor status, and initial treatment [radiation, chemotherapy, and endocrine therapy]). We used multivariable Cox proportional hazards regression to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) adjusting for breast cancer risk factors and clinical characteristics for the first breast cancer. Results: During 6.4 median years of follow-up, 442 women developed CBC (72% invasive). An increasing trend in CBC risk by age at diagnosis (p-trend=0.01) and a decreasing trend in CBC risk by year of diagnosis (p-trend=0.001) were observed. Women who received endocrine therapy had a 33% lower risk of CBC compared to women without endocrine therapy (HR=0.67, 95% CI=0.52-0.86). No associations between lifestyle and reproductive factors and CBC risk were found. Similar patterns of association were observed when analyses were restricted to women with invasive first breast cancers. Conclusions: Clinical characteristics for the first breast cancer – independent of pre-diagnostic lifestyle and reproductive factors- were the strongest risk factors for CBC in this population of older postmenopausal breast cancer survivors.

Keywords: second breast cancer, breast cancer risk factors, postmenopausal women

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