Question: Does a lack of exercise increase my risk for breast cancer?
Answer: Many people advocate exercise as a way of better health and, by extension, a way of reducing cancer risks. There are some studies that have implicated physical activity and decrease in breast cancer risk as well as other types of cancer. I think it's part of a good overall approach to health, rather than something specific to breast cancer. And, again, people who exercise more may be thinner and have less hormones in their body as a result of that, and consequently (they have) a lesser breast cancer risk -- again, tying biology to activity.
That's really the extent of our knowledge, or at least again the magnitude of risk is rarely very large in these types of studies. Exercise is probably good for your heart, it's probably good for your lungs, it's probably good for your general health, and it certainly won't hurt with respect to breast cancer risk.