Breast cancer biologic and etiologic heterogeneity by young age and menopausal status in the Carolina Breast Cancer Study: a case-control study.

BACKGROUND: Young-onset breast cancer (<40 years) is associated with worse prognosis and higher mortality. Breast cancer risk factors may contribute to distinct tumor biology and distinct age at onset, but understanding of these relationships has been hampered by limited representation of young women in epidemiologic studies and may be confounded by menopausal status. METHODS: We examined tumor characteristics and epidemiologic risk factors associated with premenopausal women's and young women's breast cancer in phases I-III of the Carolina Breast Cancer Study (5309 cases, 2022 control subjects). Unconditional logistic regression was used to assess heterogeneity by age (<40 vs. ≥40 years) and menopausal status. RESULTS: In both premenopausal and postmenopausal strata, younger women had more aggressive disease, including higher stage, hormone receptor-negative, disease as well as increased frequency of basal-like subtypes, lymph node positivity, and larger tumors. Higher waist-to-hip ratio was associated with reduced breast cancer risk among young women but with elevated risk among older women. Parity was associated with increased risk among young women and reduced risk among older women, while breastfeeding was more strongly protective for young women. Longer time since last birth was protective for older women but not for young women. In comparison, when we stratified by age, menopausal status was not associated with distinct risk factor or tumor characteristic profiles, except for progesterone receptor status, which was more commonly positive among premenopausal women. CONCLUSIONS: Age is a key predictor of breast cancer biologic and etiologic heterogeneity and may be a stronger determinant of heterogeneity than menopausal status. Young women's breast cancer appears to be etiologically and biologically distinct from that among older women.

Racial differences in physical activity among breast cancer survivors: implications for breast cancer care.

BACKGROUND: Physical activity after breast cancer diagnosis is associated with improved survival. The current study examined levels of and changes in physical activity after breast cancer diagnosis, overall and by race. METHODS: Phase 3 of the Carolina Breast Cancer Study assessed both pre- and postdiagnosis physical activity levels in a cohort of 1735 women aged 20 years to 74 years who were diagnosed with invasive breast cancer between 2008 and 2011 in 44 counties of North Carolina. Logistic regression and analysis of variance were used to examine whether demographic, behavioral, and clinical characteristics were associated with activity levels. RESULTS: Only 35% of study participants met current physical activity guidelines after diagnosis with breast cancer. A decrease in activity after diagnosis was reported by 59% of patients, with the average study participant reducing their activity by 15 metabolic equivalent task (MET) hours (95% confidence interval [95% CI], 12 MET hours-19 MET hours). After adjustment for potential confounders, when compared with white women, African American women were less likely to meet national physical activity guidelines after diagnosis (odds ratio, 1.38; 95% CI, 1.01-1.88) and reported less weekly postdiagnosis physical activity (12 MET hours vs 14 MET hours; P = .13). In adjusted stratified analyses, receipt of treatment was found to be significantly associated with postdiagnosis activity in African American women (P < 0.01). CONCLUSIONS: Despite compelling evidence demonstrating the benefits of physical activity after a diagnosis of breast cancer, it is clear that more work needs to be done to promote physical activity in patients with breast cancer, especially among African American women.