Physical activity has no relation with the risk of developing in situ breast cancer, according to an analysis of the association between physical activities and in situ, or noninvasive, breast cancer. After more than 11 years of following a European cohort of 283,827 women, 1,059 of whom had in situ cancer, the authors of a recently published study also found no association depending on exercise type.

Further, the results did not vary between women of pre- and postmenopausal age or between obese and nonobese women. In the case of invasive cancer, epidemiologic studies have demonstrated that exercise is associated with a lesser risk.

“The etiology of in situ breast cancer could be different to that of invasive breast cancer, or rather physical activity has a protective effect only in later stages of the carcinogenesis process. This would explain why no association has been found in non-invasive breast cancer,” said María José Sánchez Pérez, MD, PhD, Director of the Granada Cancer Registry and one of the authors of the study. This study was published in Cancer Epidemiology, Biomarkers & Prevention (2012; doi:10.1158/1055-9965.EPI-12-0961).

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An in situ ductal carcinoma of the breast is the most frequent form of noninvasive breast cancer in women and is a risk factor or precursor for the development of invasive breast cancer. Therefore, the association between physical activity and this cancer would indicate that exercise could act as a protective factor in the early stages of the carcinogenesis process. However, this is not found to be the case.

A previous study carried out on the same cohort investigated the association between physical activity and the risk of developing invasive breast cancer. It found that physically active menopausal women have a 14% less chance of developing this cancer compared to their sedentary menopausal counterparts.

The results revealed that the risk of developing breast cancer is reduced 8% by moderate physical activity and 14% by intense physical activity. This effect was similar for recreational physical activity and domestic chores.

In fact, the World Cancer Research Fund published an expert report that confirmed that there is enough evidence on the protective effects of physical activity, and stated that this evidence is somewhat more convincing in the case of menopausal women.

The current primary approach to reduce the incidence of breast cancer is prevention. “The risk factors associated with breast cancer are obesity in menopausal women and alcohol consumption, whereas physical activity and breastfeeding provide protection against the development of this cancer,” concluded Sánchez.