Exercise may improve the prognosis of prostate cancer patients by affecting blood vessels in their tumours, a study suggests.
Researchers found that men who walked at a fast pace before being diagnosed with the disease had tumours containing larger and more regularly shaped blood vessels.
Better formed tumour blood vessels may in turn inhibit cancer aggressiveness and promote better responses to treatments, the scientists believe.
Physically active men with prostate cancer have a lower risk of recurrence and death from the disease than those living sedentary lives, but until now the reason has remained a mystery.
The new study looked at 572 prostate cancer patients taking part in a US lifestyle and health investigation called the Health Professionals Follow-up Study.
Men with the fastest walking pace - between 3.3 and five miles per hour - prior to diagnosis had 8% more regularly shaped tumour blood vessels than the slowest walkers who ambled at 1.5 to 2.5 mph.
"Prior research has shown that men with prostate tumours containing more regularly shaped blood vessels have a more favourable prognosis compared with men with prostate tumours containing mostly irregularly shaped blood vessels," said lead scientist Dr Erin Van Blarigan, from the University of California at San Francisco.
"In this study, we found that men who reported walking at a brisk pace had more regularly shaped blood vessels in their prostate tumors compared with men who reported walking at a less brisk pace.
"Our findings suggest a possible mechanism by which exercise may improve outcomes in men with prostate cancer. Although data from randomised, controlled trials are needed before we can conclude that exercise causes a change in vessel regularity or clinical outcomes in men with prostate cancer, our study supports the growing evidence of the benefits of exercise, such as brisk walking, for men with prostate cancer."
The results were presented at the American Association for Cancer Research - Prostate Cancer Foundation Conference on Advances in Prostate Cancer Research in San Diego, US.
Activity and walking pace were assessed every two years as part of the on-going study, starting in 1986.
In a summary of their work the researchers concluded: "Brisk walking may be associated with more regularly shaped vessels in prostate tumours. Normalisation of tumour vasculature may in turn inhibit tumour aggressiveness and improve response to anticancer therapies.
"Future studies should investigate whether increasing brisk walking after diagnosis is associated with favourable changes in tumour vasculature."
Dr Matthew Hobbs, deputy director of research at Prostate Cancer UK said: "Although this research provides a plausible explanation of how exercise might improve outcomes for men with prostate cancer, much more research is needed to confirm the impact of lifestyle factors on men's recovery.
"We hope that further research in this area may one day give us a way to improve the prognosis for the 40,000 men in the UK who are diagnosed with prostate cancer each year. In the meantime, however, we do know that exercising regularly is good for our health in a general sense, so we would certainly recommend that all men should try to be as physically active as possible."