Physical activity may improve prostate cancer prognosis
Dr Ying Wang - American Cancer Society, Atlanta, USA
Although evidence is still limited, previous studies suggest that vigorous activity and brisk walking after prostate cancer diagnosis is associated with a lower risk of dying from the disease. What we still don’t know is if physical activity prior to prostate cancer diagnosis is associated with a risk or not. This is also important because there’s a concern that the inverse association we saw with the post-diagnosis physical activity is partially due to reverse causation because patients with advanced disease may reduce their physical activity levels, especially vigorous activity. In contrast, the pre-diagnosis physical activity is not subject to a reverse causation and may represent a long-term behaviour. More importantly, pre-diagnosis physical activity might be associated with the factors that can affect tumour aggressiveness. Walking, as the most common type of physical activity is also interesting and has been evaluated in previous studies, however, it was not examined in the absence of other activities.
In this study we are also interested in looking at the association between sitting time and risk of dying from prostate cancer. So therefore in this large prospective cohort study we investigated the physical activity of walking only in the absence of other activities and the sitting time, both before and after prostate cancer diagnosis in relation to the risk of prostate cancer specific mortality. What we saw is men with higher physical activity levels after diagnosis had a significantly lower risk of dying from disease compared with men with a minimum level of physical activity which is equivalent to less than one hour of walking per week. We also saw a similar beneficial association for pre-diagnosis physical activity levels which suggest that the inverse association we saw with the post-diagnosis physical activity is not purely due to reverse causation.
We were able to evaluate walking only in the absence of other activities because approximately 40% of patients in this study reported that walking is the only form of recreational physical activity they did. What we saw is very interesting, it’s that men who walked 4-6 hours per week prior to prostate cancer diagnosis had a significantly lower risk of dying from prostate cancer and men who walked 7 hours per week had an even greater reduced risk. However, we didn’t see any association for post-diagnosis and walking only.
Is there concluding evidence to suggest that walking has beneficial effects?
It’s still too early to conclude there’s no beneficial effect and there is still limited evidence suggesting any biological mechanisms behind this finding. But the original study conducted by a group of researchers in Harvard found that brisk walking prior to prostate cancer diagnosis is associated with more normally shaped blood vessels in prostate tumours. The normally shaped blood vessels in prostate tumours can inhibit the cancer spread in the body and may lower the risk of dying from the disease.
How do you see exercise affecting patient survival?
Currently the American Cancer Society recommends that cancer survivors engage in a minimum of 150 minutes moderate intensity activities or 75 minutes vigorous intensity activities per week. So our results suggest that prostate cancer patients should adhere to these guidelines for better survival outcomes and physicians should consider promoting adopting a physically active lifestyle to their prostate cancer patients.
What hopes do you have for treatment in the near future?
What will be interesting is to investigate the tumour characteristics in prostate cancer tumour biopsies so that we can identify potential biological mechanisms behind this finding.