Included are genes known to suppress tumor growth and repair DNA, which  might mean that exercise could prevent or delay progression of the  disease, the researchers said.

“There are many reasons to exercise,” June Chan, associate professor of  epidemiology and biostatistics, and urology at the University of  California, San Francisco, said during a Tuesday press conference. “Here’s  yet another great reason to exercise and it may offer a prostate  cancer-specific benefit.”

For the study, Chan’s team compared prostate genes from 70 men with  low-risk prostate cancer to normal prostate genes from 70 men.

The cancer patients in the study were undergoing “active  surveillance” — also known as “watchful waiting” — rather than active  treatment.

The men answered questions about how much and what type of exercise  they did.

Chan’s group found 184 genes that were differently expressed in men who  did activities such as jogging, tennis or swimming for at least three  hours a week, compared with genes in men who did less exercise.

Genes more highly expressed in men who did vigorous exercise included  well-known tumor-suppressor genes associated with breast cancer, BRCA1 and  BRCA2, the researchers found.

In addition, these men also had increased expression of genes involved  in DNA repair, they noted.

The researchers hope to confirm their findings in a larger group of men  who are undergoing active surveillance, and also among men who have  experienced a recurrence of their cancer.

There are limitations to this study, Chan said. Most important, the  study was small and so the results could be by chance, she said.

“If confirmed, the results suggest that vigorous physical activity  might offer protection against prostate cancer progression,” Chan said.

Exercise has also been found to have benefits for breast and colon  cancer, the researchers noted.

The results of the new study are slated for presentation Friday at a  meeting of  the American Society of Clinical Oncology in San  Francisco.

Because this research is being presented at a medical meeting, the data  and conclusions should be viewed as preliminary until published in a  peer-reviewed journal.

Dr. Anthony D’Amico, chief of radiation oncology, and a prostate cancer  expert from Brigham and Women’s Hospital in Boston, said that “this is an  interesting, hypothesis-generating study that will require further testing  and perhaps opens doors to exercise as part of future prostate cancer  treatment, but it’s too soon to tell.”

In two studies last year, Chan’s group found links between vigorous  activity, such as brisk walking, and a lowered risk of prostate cancer  progression and death.

In one study, which appeared in the February 2011 Journal of  Clinical Oncology, men with prostate cancer who participated in three  or more hours a week of vigorous activity had about a 50 percent lower  risk of death from all illnesses, and a 60 percent lower risk of death  from prostate cancer, compared to men who participated in less than one  hour per week of vigorous physical activity, Chan said.

In the other study, published in the May 2011 issue of Cancer  Research, men who walked three miles per hour or faster had about half  the risk of prostate cancer progression of men who walked at two miles per  hour or less, she said.

“These studies suggested that some form of cardiopulmonary exercise  might offer specific benefits for prostate cancer,” Chan said. “However,  the molecular mechanisms by which physical activity exerts this effect on  prostate cancer remains unknown.”