Another reason exercise is good for you: A large study found that men who exercise after a diagnosis of prostate cancer (but which is not metastatic) had a lower risk of dying from prostate cancer - as compared to those men who don't exercise.
So get out there and do something that gets you moving - and yes, walking is an exercise (Note: 1 mile = 20 minutes of walking, thus 3 miles = 1 hour).
In this study the average age at diagnosis was 71, but studies find that exercise has numerous benefits at all ages. Some doctors even think of exercise as "anticancer therapy" (here, here). Also, exercise has anti-inflammatory benefits, and current thinking is that chronic inflammation is linked to cancer.
The American Cancer Society in its cancer prevention guidelines recommends that adults should be physically active, and get at least 150 minutes of moderate physical activity or 75 minutes of vigorous intensity activity each week (or a combination of these), preferably spread throughout the week.
From Medscape: Exercise Linked to Lower Mortality With Early Prostate Cancer
Men with nonmetastatic prostate cancer may have longer survival the more they exercise, a recent study suggests. For these men, regular moderate or vigorous physical activity was associated with 31 percent to 37 percent lower likelihood of death during the study, compared to more modest amounts of exercise.
“This confirms and expands on previous work that shows an inverse association between recreational physical activity after diagnosis and risk of prostate cancer-specific mortality,” said lead study author Ying Wang of the American Cancer Society in Atlanta, Georgia, in email to Reuters Health.
Wang and colleagues pulled data from a large, long-term study group established by the American Cancer Society in 1992, focusing on 7,000 men who were diagnosed with prostate cancer between 1992 and 2011. The average age at cancer diagnosis was 71, and there were 2,700 deaths through 2012, including 450 due to prostate cancer and 750 due to heart disease. The average time from diagnosis to death was about eight years for those who died from cancer and 10 years for those who died from other causes.
Men who were more active before diagnosis were more likely to have lower-risk cancer tumors and a history of prostate screenings. They were also leaner, more likely to be nonsmokers and vitamin users and they ate more fish. Both before and after diagnosis, walking accounted for 73 percent of the physical activity that men did, followed by 10 percent for cycling and 5 percent for aerobic exercise, according to the report online now in European Urology.
Based on exercise levels before diagnosis, moderate to vigorous exercise, including walking, was linked to lower risk of death from prostate cancer, but only for men with lower-risk tumors. But after the diagnosis, the same levels of exercise were linked to lower risk of death from prostate cancer for all men, although the apparent benefit of walking was no longer statistically meaningful. [Original study.]