A cancer diagnosis can be a devastating event — but some may also be preventable. In fact, an estimated half of all cancer deaths are avoidable by practicing healthy lifestyle habits, according to the American Cancer Society.

One of the most potent cancer-fighting weapons is exercise. While the benefits of a regular fitness program include keeping the pounds off, improving blood pressure and mental outlook, exercise can also halt the onset of some diseases. Several studies have shown that physical activity is linked with decreased risk of some cancers, particularly breast and colon cancer.

It is never too late to begin a fitness program, said Dr. Priscilla Furth, a professor of oncology at Georgetown University Medical Center's Lombardi Comprehensive Cancer Center.

“The good news is that it doesn't matter [when you begin], in that you will see a benefit from exercise at whatever age you are,” Furth said.

Here are seven cancers that scientific research has shown can be stalled by exercise: