1.Recreational activity and prostate cancer specific mortality
Several studies have suggested that higher levels of physical activity are associated with a lower risk of dying from colorectal or breast cancer. This has also been highlighted for prostate cancer, although the potential for reverse causation bias – that ill health was the cause of lower physical activity - has limited interpretation of these results.
A study published in European Urology this month revisited this topic and analysed the recreational activity of 10,864 men, to examine the reported association of pre- and post-diagnosis physical activity with prostate cancer specific mortality. The study focused on aerobic exercise and the amount of physical activity per week during the past year was self-reported via questionnaire. Pre-diagnosis physical activity was calculated from the last questionnaire completed at least 1 year prior to diagnosis, and the post-diagnosis activity calculated from the first questionnaire completed at least 1 year after diagnosis. The median age at diagnosis was 71 years (interquartile range: 67-75 years), and deaths were ascertained from the national death index. To reduce reverse causation bias, deaths occurring within four years of the post-diagnosis questionnaire were excluded.
Pre-diagnosis physical activity was taken as a surrogate measurement of long-term physical activity (n=7328). When controlling for age, cancer status, family history, race and lifestyle factors (including PSA test history, BMI, smoking status and diet) there was a statistically significant inverse association between prediagnosis recreational physical activity and prostate cancer specific mortality amongst men with low-risk tumours (p=0.03). Furthermore, men with low-risk tumours who walked for more than 7 hours per week had a 47% less risk of prostate cancer specific mortality compared with those who walked 1-3 hours per week (HR: 0.53, 95% CI: 0.33-0.86), p=0.04). High levels of physical activity were also associated with a 20% lower risk of cardiovascular disease specific mortality (HR: 0.80, 95% CI: 0.67-0.96, p=0.008) and a 12 % lower risk for all-cause mortality (HR: 0.88, 95% CI: 0.80-0.97, p<0.0001).
When adjusted for treatment, family history, cardiovascular disease history, smoking status, BMI, age and PSA test frequency, high levels of post-diagnosis recreational activity were associated with a significantly lower risk of prostate cancer specific mortality (HR: 0.69, 95% CI: 0.49-0.95, p=0.006) (n=5309), and were also associated with a 14% lower risk of all-cause mortality (HR:0.86, 95% CI: 0.75-0.98, p<0.0001).
Limitations of this study include potential measurement error from one-time self-reported physical activity, and positive confounding by severity of disease at diagnosis cannot be excluded. Also, a lack of information on treatment completion date, adverse effects from treatment, adjuvant therapies and tumour recurrence limited analysis control. However, the study supports the importance of ongoing and future clinical trials to assess impact of physical activity on tumour progression.