Abstract 865: Physical inactivity increases the risk of endometrial cancer and premenopausal breast cancer

Abstract Background. Epidemiological studies indicate that physical activity reduces the risk of cancer. Physical inactivity or sedentary behavior, has recently been suggested as a risk factor independent of physical activity level. Breast and endometrial cancer incidence have both been associated with physical activity, and endometrial cancer incidence with physical inactivity/sedentary behavior. The purpose of the present study was to investigate physical inactivity as a risk factor for breast cancer, divided into pre- and postmenopausal subtypes, and for endometrial cancer, and to explore possible dose-response relations regarding the level of physical inactivity. Methods. In a population-based prospective cohort study, 29 520 women in the southern part of Sweden, in ages between 25 and 64 years, participated. A questionnaire-based survey was performed 1990-92. Their reported professions were classified as sedentary or not which together with reported participation in competitive sports constituted the basis for classification into three activity-levels; (1) physical inactivity, defined as having sedentary occupation and no participation in competitive sports, (2) partly inactive, defined as either having a sedentary occupation or non- participation in competitive sports, (3) Physical active, defined as not having a sedentary occupation and participation in competitive sports. The association between physical inactivity and pre and postmenopausal breast and endometrial cancer incidence were analyzed by Cox regression, adjusted for hormonal factors, family history of cancer, body mass index (BMI) and age. Results. Physical inactive women had a significantly increased risk of endometrial cancer (HR = 2.41, 95% CI 1.14-5.11) and premenopausal breast cancer (HR = 2.40, 95% CI 1.14-5.02), compared with women who were less physical inactive. No such association was found for postmenopausal breast cancer. Analysis of linear trend showed a significant dose-response relationship with increased risk of both premenopausal breast cancer (ptrend 0.02) and endometrial cancer (ptrend <0.01). Conclusions. In the current study we found an increased incidence of premenopausal breast cancer and endometrial cancer in physical inactive women and a linear trend indicating dose-response relationship. Not only physical activity but also the avoidance of physical inactivity may reduce the risk of premenopausal breast cancer and endometrial cancer. Citation Format: Anna Johnsson, Per Broberg, Anders Johnsson, Åsa Tornberg, Håkan Olsson. Physical inactivity increases the risk of endometrial cancer and premenopausal breast cancer. [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 865. doi:10.1158/1538-7445.AM2015-865