Physical activity has been identified as protective factor for invasive breast cancer risk in several studies, whereas studies on in situ carcinoma are rare. Studies investigating whether this association is valid for all breast cancer subtypes defined by the estrogen receptor (ER) and the progesterone receptor (PR) status yielded inconsistent results.

Material and methods: The study is based on data from 283,680 female participants from the multinational EPIC-cohort study, for whom detailed information on recreational household and occupational physical activity as well as smoking habits, dietary habits, anthropometry and socio-demographic variables were assessed at the baseline examination between 1992 and 2000. Adjusted hazard ratios (HR) were estimated by proportional hazards models. For outcome variables with more than 2 levels competing risk models were applied. During a median follow-up period of 11.7 years, 9,947 incident breast cancer cases were identified, including 1,060 carcinoma in situ. Out of the 8,887 invasive breast cancer cases the estrogen receptor status, the progesterone receptor status and the combined status of the tumor could be assessed for 6,007 (67.6%), 4,814 (54.2%), and 4798 (53.9%) cases, respectively.

Results: For invasive tumors, breast cancer risk was inversely associated with high levels of total physical activity (HR=0.85, 95% confidence interval (CI): 0.77–0.93, p-trend<0.001) and of recreational activity (HR=0.88, 95%-CI: 0.82–0.94, p<0.001), comparing the highest to the lowest activity quartile. Effects for postmenopausal breast cancer (HR=0.81, 95%-CI: 0.70–0.93, p=0.002 for total physical activity, HR=0.89, 95%-CI: 0.81–0.97, p=0.005 for recreational activity) were slightly stronger than for premenopausal breast (HR=0.87, 95%-KI: 0.72–1.04, p=0.082 for total physical activity, HR=0.84, 95%-KI 0.72–0.98, p=0.032 recreational activity). The analyses by hormone receptor status indicated differential effects with stronger effects of total physical activity for hormone receptor positive (ER+/PR+) breast tumors, compared to the other combinations (p-value for test of heterogeneity: p=0.043). More detailed analyses showed that primarily the PR status (p-heterogeneity: 0.006) rather than the ER status (p-heterogeneity 0.235) dominated this result. For in situ carcinoma no associations for any of the physical activity variables were found.

Conclusions: The protective effects for physical activity on breast cancer risk could be confirmed. The results of this largest prospective study on physical activity and different hormone receptor status indicate that physical activity primarily reduces the risk for PR+ and ER+/PR+ tumors. The result strengthens the hypothesis that the reduction of breast cancer risk by physical activity is at least partly related to hormonal pathways.

Citation Information: Cancer Prev Res 2011;4(10 Suppl):PR-04.

Copyright © American Association for Cancer Research
2011