Physical Inactivity & Hormone Therapy Increase Population-Level Breast Cancer Risk
Posted Jan 26 2011 10:02am
Numerous breast cancer studies have explored lifestyle factors, both modifiable and non-modifiable, that increase breast cancer risk. However, only a few of these studies have determined what percent of breast cancer cases could have been prevented by removing a breast cancer risk factor from a population and fewer still have explored the impact of removing multiple breast cancer risk factors.
A new breast cancer research study examined the impact of multiple risk factors, both non-modifiable (age at puberty, age at menopause, number of births, etc.) and modifiable (exercise, hormone therapy use, alcohol consumption, body mass index), on breast cancer risk at the population level. In order to determine the impact of these risk factors, the study investigators analyzed data from over 3,000 breast cancer cases and over 6,300 control women. The researchers calculated the odds of developing breast cancer for each risk factor and the percent of breast cancer cases that could be attributed to specific risk factors. In addition to doing this for overall invasive breast cancer, the study investigators conducted this analysis on breast cancer subtypes defined by hormone receptor status. The results of these analyses are outlined below.
Non-Modifiable Breast Cancer Risk Factors
Of the non-modifiable risk factors, a family history of breast cancer, benign breast disease, only having one child, puberty before 14 years of age, and menopause at 50 years of age or older were all linked to an increased risk of breast cancer.
These non-modifiable risk factors accounted for 37% of overall invasive breast cancers, 37% of ER+/PR+ breast cancers, 48% of ER+/PR- breast cancers, and 31% of ER-/PR- breast cancers.
Modifiable Breast Cancer Risk Factors
Use of hormone therapy, particularly combined estrogen + progesterone (E+P) therapy, nearly doubled breast cancer risk on average and accounted for 19% of overall invasive breast cancers, 25% of ER+/PR+ breast cancers and 18% of ER+/PR- breast cancers. However, E+P therapy was not linked to ER-/PR- breast cancers.
A lack of physical activity was linked to 13% of overall breast cancers, 17% of ER+/PR+ breast cancers, and 11% of ER-/PR- breast cancers, but was not linked to ER+/ER- breast cancers.
The combination of hormone therapy use and physical inactivity accounted for 30% of overall invasive breast cancers, 38% of ER+/PR+ breast cancers, 20% of ER+/PR- breast cancers, and 10% of ER-/PR- breast cancers.
While the results of this study are not necessarily surprising, there is some valuable and interesting information presented. First, this study confirms the major impact that hormone therapy use and lack of exercise has on breast cancer risk and additionally shows that it is true at the population level as well. It is interesting and important to note that these two modifiable breast cancer risk factors combined account for nearly as much breast cancer incidence as do the 5 main non-modifiable risk factors combined. This shows us that removing or at last minimizing these two risk factors has the potential to decrease breast cancer incidence in a population by 30% overall and by nearly 40% for ER+/PR+ breast cancers. Second, this research clearly shows that different hormone-receptor breast cancer subtypes are affected by breast cancer risk factors differently. Determining which risk factors impact which types of breast cancer remains an important aspect of our fight against breast cancer so that individual and effective strategies to fight breast cancer can be developed.