UC Irvine

Abstract: Background. Evidence has accumulated showing that physical activity reduces breast cancer risk. Whether risk reduction pertains to all breast cancer or specific receptor-defined subtypes is unclear. Moreover, few studies have examined whether changes in the amount of physical activity during adulthood influence breast cancer risk. Methods. Among 108,907 women, ages 22 to 79 years with no history of breast cancer when they joined the California Teachers Study in 1995-1996 (baseline), 5,578 women were diagnosed with invasive breast cancer during follow-up through December, 2011. Subtypes were defined by the expression status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Cox proportional hazards models were fit to data to estimate adjusted hazard rate ratios (HRs) and 95% confidence intervals (CIs) associated with long-term and recent (within 3 years of baseline) recreational physical activity. Among 54,690 women who provided updated information on physical activity in 2005-2008, we also assessed whether changes in the level of physical activity since baseline influenced breast cancer risk (654 cases diagnosed during follow-up). Results. Long-term and recent recreational physical activity were inversely associated with risk of triple negative breast cancer (TNBC, both Ptrend ≤ 0.05), but not other subtypes (all Ptrend ≥ 0.07). The reduced risk of TNBC was limited to strenuous physical activity. A 50% (HR = 0.50, 95% CI = 0.29-0.86) lower risk of TNBC was observed among women in the highest (≥5.01 h/wk) versus lowest category (≤0.50 h/wk) of long-term strenuous recreational physical activity; this was not modified by baseline body mass index (<25 kg/m2 vs. ≥25 kg/m2), menopausal hormone therapy (MHT) use (never vs. ever), or the cessation of MHT use (former vs. recent). An inverse association between strenuous recreational physical activity and risk of luminal A-like (ER+ or PR+ plus HER2-) breast cancer was observed only among former MHT users (Ptrend: 0.02 for both long-term and baseline strenuous physical activity). Women who increased their level of recent recreational physical activity from ≤0.50 h/wk at baseline to ≥4.51 h/wk in 2005-2008 had a 32% (HR = 0.68, 95% CI = 0.47-0.99) lower risk of breast cancer overall than those who stayed at the lowest level. Conclusions. This study suggests that long-term strenuous physical activity is associated with lower risk of TNBC. Further, it shows that substantially increasing the amount of total recreational physical activity in adulthood decreases the risk of breast cancer. Citation Format: Huiyan Ma, Jessica Clague, Xinxin Xu, Yani Lu, Kayo Togawa, Sophia S. Wang, Christina A. Clarke, Eunjung Lee, Hannah L. Park, Jane Sullivan-Halley, Susan Neuhausen, Leslie Bernstein. Long-term and recent recreational physical activity reduces risk of triple negative and other subtypes of invasive breast cancer in the California Teachers Study. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 872. doi:10.1158/1538-7445.AM2015-872