THE EFFECT OF ADIPOSITY ON DISEASE OUTCOMES IN WOMEN WITH BREAST CANCER
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There is accumulating evidence that obesity has a significant role in breast cancer (BC) prognosis. Among women with BC, obesity at diagnosis and weight gain after diagnosis may increase risk for BC recurrence and death, and other chronic diseases. Few studies have examined the impact of tumor subtype, menopausal status and race on obesity and disease outcomes in women with BC. In this thesis we addressed the following questions: Are women with BC at increased risk for weight gain after diagnosis compared to cancer-free women? What is the effect of obesity at diagnosis on BC mortality, among pre- versus postmenopausal women, and those with different tumor subtypes? Is this relationship the same in black and white women? First we prospectively examined weight gain over four years in 303 BC survivors compared to 307 cancer-free women, matched on age and menopausal status, from the same familial risk cohort. We found that BC survivors gained significantly more weight than cancer-free women, and that survivors treated with chemotherapy were more than twice as likely to gain at least 11 pounds, an amount of weight gain that increases risk for coronary heart disease and diabetes. Next, we used data from the National Comprehensive Cancer Network (NCCN) Breast Cancer Outcomes database to prospectively study the association between obesity at diagnosis and BC mortality, by menopausal status, tumor subtype, and race, among 18,600 women diagnosed with invasive early stage BC. In premenopausal women, obesity was significantly associated with increased mortality across all four tumor subtypes (Hormone receptor positive, Hormone receptor negative, HER2 positive and triple negative), whereas among postmenopausal women, obesity increased risk only among women with Hormone Receptor positive disease. Finally, in race-stratified estimates we showed that obesity increased BC mortality significantly in both black and white premenopausal women, after adjusting for comorbidities, access to care, and stage at diagnosis. Our results highlight the importance of monitoring weight in all women with BC as an approach to reducing mortality from the cancer itself and other chronic diseases. This is another reason why Public Health efforts to reduce obesity in the US should be strongly encouraged.