Regular exercise and prostate cancer-specific survival
Posted Jan 06 2011 12:00am
According to a new analysis of data from participants in the Health Professionals Follow-Up Study, regular physical activity is associated with an overall and a prostate cancer-specific survival benefit in men initially diagnosed with prostate cancer who show no signs of metastasis at diagnosis. However, these benefits appear to be limited to men who survive for at least 5.5 years after their initial diagnosis, as we shall discuss below.
[Please note that some important revisions have been made to this report since it was originally posted early this morning. We have now had the chance to review the entire text of this paper.]
The study by Kenfield et al. , just published on line in the Journal of Clinical Oncology, was designed to evaluate physical activity among 2,705 men in the Health Professionals Follow-Up Study initially diagnosed with non-metastatic prostate cancer and observed between 1990 and 2008, with assessments every 2 years.
In assessing the data in this report, it is important to understand that, of the 3,032 men who were theoretically eligible for inclusion in this study, the authors excluded 327, “to reduce the impact of advanced disease on activity duration and intensity.” These patients fell into one of four categories:
107 had metastatic prostate cancer at the time of initial diagnosis.
200 died within 4 years of their first post-diagnostic activity assessment.
7 reported metastatic disease after initial diagnosis but before their first post-diagnostic activity assessment.
13 reported metastatic disease within 2 years of their first post-diagnostic activity assessment
This left 2,705 men who met eligibility criteria for evaluation in this study.
It is also important to understand that the median time from initial diagnosis to initial post-diagnostic activity assessment was 18 months.
The results reported by Kenfield and her colleagues are as follows:
548/2,057 men (20.2 percent) died after their post-diagnosis physical activity assessment.
112/548 men who died (20.4 percent) actually died of prostate cancer.
The median duration of follow-up for the survivors was 9.7 years.
The median duration of follow-up for the men who died (of all causes) was 7.8 years.
The men who were physically active had a statistically significantly lower risk of all-cause mortality.
Both non-vigorous activity and vigorous activity were associated with significantly lower overall mortality.
Men who walked for at least 90 min/week at a normal to very brisk pace had a 46 percent lower risk of all-cause mortality (hazard ratio [HR] = 0.54), as compared with men who walked for shorter durations at an easy walking pace.
Men who participated in vigorous activity for at least 3 h/week had a 49 percent lower risk of all-cause mortality (HR = 0.51)
Men who participated in vigorous activity for at least 3 h/week had a 61 percent lower risk of prostate cancer-specific mortality (HR = 0.39), as compared with men who participated in less than 1 h/week of vigorous activity.
Men who exercised vigorously before and after a diagnosis of non-metastatic prostate cancer had the lowest risk of all-cause and prostate cancer-specific mortality within the study period.
The authors conclude that a modest amount of vigorous activity such as biking, tennis, jogging, or swimming for at least 3 hours a week may substantially improve prostate cancer-specific survival.
There is extensive coverage of this study in a HealthDay report , issued yesterday. In that report, Dr. Kenfield is quoted as saying that, “This is the first study in men with prostate cancer to evaluate physical activity after diagnosis in relation to prostate cancer-specific mortality and overall mortality.”
According to the HealthDay report, all patient activities investigated in the course of the study were given a “metabolic equivalent task” or MET value, based on the amount of energy required for each activity relative to just sitting down. Non-vigorous activities had a MET value of < 6; vigorous activities were given MET values of 6 and higher. Kenfield and her colleagues then estimated how many MET hours per week were expended by each patient based on the nature and pace of each activity they engaged in. Activities that were assessed included walking, jogging, running, bicycling, swimming, rowing, stair-climbing, weight-lifting, arduous outdoor work, and playing tennis, squash, racquetball and/or golf.
This study followed patients for up to a maximum of 18 years in total, which should be sufficient follow-up to be able to confirm effects on both overall and prostate cancer-specific mortality. However, in interpreting these results, it is important to understand that the authors effectively excluded any patient with a survival of less than 5.5 years from time of diagnosis because the median time from diagnosis to initial activity assessment was 18 months and then they further excluded any man who lived for less than 4 years after that initial activity assessment.
The fact that even relatively mild exercise offers prostate cancer patients an overall survival benefit is hardly surprising, because of the well-understood, general benefit of exercise on cardiovascular and immunological health. However, if there really is a prostate cancer-specific mortality benefit on top of the overall mortality benefit for men with non-metastatic prostate cancer and a projected survival of about 5.5 years or more from the time of diagnosis, this is extremely important, and it would be good to have some clarity on just how much longer that survival benefit might be (3 months or 3 years?). It is also worth noting that greater overall survival benefit was associated with more vigorous exercise over at least 10 hours a week. In other words, regardless of one’s risk of prostate cancer-specific mortality, one’s greatest potential benefit came from ensuring 10+ hours of relatively vigorous exercise each week (e.g., walking at at least a “brisk” pace).