A new international study led by researchers at Mount Sinai Hospital, published recently in the Journal of the National Cancer Institute, shows that close to 50 per cent of the men studied posthumously harboured prostate cancer over the age of 60, but had died of other causes. The study provides further evidence that a large proportion of prostate cancer tumours are not destined to become life-threatening.
Led by Dr. Alexandre Zlotta, Director of Uro-Oncology at Mount Sinai Hospital’s Murray Koffler Urologic Wellness Centre, a scientist with Mount Sinai’s Lunenfeld-Tanenbaum Research Institute and Professor of Surgery at the University of Toronto, the new study advocates for an improved screening method that can detect cancers based on their clinical significance and level of aggressiveness, rather than screening for all forms of this disease. The current widespread use of prostate-specific antigen (PSA) testing in North America for the disease increases the likelihood of the over-detection of low-risk prostate cancers, which can potentially lead to unnecessary treatment that may result in major lifestyle and emotional side effects for patients.
“The study emphasizes the importance of understanding how many men in North America over a certain age harbour the latent form of prostate cancer, as this population is often over-diagnosed and over-treated,” says Dr. Alexandre Zlotta. “But our study shows that in Japan, despite completely different lifestyles, despite a much lower incidence of clinically detected prostate cancer, and a much lower mortality rate due to prostate cancer compared to men in North America, Asian men have similar prevalence of the disease – but they aren’t dying from it.”
In the study, researchers studied autopsied Caucasian men in Russia, who share environmental characteristics with North American men, such as reduced sun exposure and a high-fat diet, both of which have been implicated in increased risk for prostate cancer. At the same time, the study also looked at autopsied Asian men in Japan, because the incidence of prostate cancer is much lower in Japan than in North America. Japanese Asian men typically have a lower death rate from prostate cancer as well as a very different diet from North American men. And contrary to North America, there is no widespread PSA screening in either Russia or Japan.
By studying these two distinct populations, the research team showed that despite the differences in incidence and mortality rates, and in genetics and lifestyle factors, the prevalence of prostate cancer was similar in both Caucasian and Asian men. In fact, the disease was even more aggressive in Asians. A subset of the autopsied prostates presented with tumor characteristics physicians would usually recommend treatment for, such as surgery or radiation, but these men had actually died of causes other than prostate cancer.
In light of this data, the study suggests that the progression of early prostate cancer, including more aggressive forms of the disease, is far from inevitable within a man’s lifetime. The study concludes that it is worth re-examining our current definitions of clinically unimportant and clinically significant prostate cancer. The study’s findings also support efforts toward a better understanding of the biology of prostate cancer.
Dr. Zlotta, who is also on staff at the University Health Network, collaborated on the study with Dr. Theodorus Van der Kwast, a pathologist at the University Health Network, along with researchers at Sunnybrook Health Sciences Centre, and scientists in Tokyo and Moscow. The study was supported by grants from Prostate Cancer Canada and GlaxoSmithKline.