It is considered an effective path to good health, but a new study has shown that exercise may lead to faster prostate tumour growth, and thus hasten the decline of some cancer patients.
Researchers at the Duke Comprehensive Cancer Center (DCCC) and the Duke Prostate Center, who looked at prostate tumours in mice, found that cancerous cells multiplied twice as quickly when the animals were active.
According to the researchers, exercise may increase blood flow to tumours and thus support their growth.
"Our study showed that exercise led to significantly greater tumor growth than a more sedentary lifestyle did, in this mouse model," said Lee Jones, Ph.D., a researcher in the DCCC and senior investigator on this study.
"Our thought is that we may, in the future, be able to use this finding to design better drug delivery models to more effectively treat prostate cancer patients, and those with other types of cancer as well," he added.
The researchers implanted prostate tumours subcutaneously in the flanks of 50 mice and then put half of the mice in cages with exercise wheels and half in cages with no wheels. All mice were fed the same diet. On average, the exercising mice ran more than half a mile each day.
"We found that among the mice that had the opportunity to voluntarily exercise, tumours grew approximately twice as fast as they did among the mice that did not have the opportunity to exercise," Jones said.
Researchers and clinicians know that a challenge in delivering chemotherapy and radiation to tumours can be their poor blood flow, so these findings may hint at a way in which to improve blood flow to tumours, perhaps then allowing for better distribution of medicine, he said.
"We're wondering, can we combine exercise with treatments such as chemotherapy, hormone therapy or radiation, to maximize the results we achieve in prostate cancer patients. That question will be the subject of subsequent studies," Jones said.
The researchers are currently conducting a validation study, in mice, in which tumours are injected directly into the prostate, thereby better simulating human prostate cancer, he added.
"Down the line, we will test this hypothesis in humans undergoing medical treatment for prostate cancer," he said.
The researchers want to caution men against interpreting these findings as an endorsement for not exercising for fear of getting or exacerbating cancer.
"These mice were not receiving treatment and we were allowing aggressive tumours to grow unchecked for the sake of the experiment. Patients would not find themselves in the same situation," said study investigator Freedland, a urologist at Duke.
Concerns should also be overridden by the well-established benefits of exercise, including its positive effects on cardiovascular health, Type II diabetes, obesity, and many other chronic conditions, he said.
This is one of the first studies to look at the physiological effects of exercise on the tumour itself, rather than examining the quality-of-life or symptom-control effects of exercise in cancer patients, Jones said.
"The findings were a bit surprising, but provide a very important and exciting foundation upon which to build," he added.
The findings were presented in a poster session at the American Association for Cancer Research annual meeting on April 13 in San Diego, Calif.