Thursday, August 23, 2012
Prostate Cancer: Six Things Men Should Know About Tomatoes, Fish Oil, Vitamin Supplements, Testosterone, PSA Tests
When it comes to prostate cancer, there's a lot of confusion about how to prevent it, find it early and the best way -- or even whether -- to treat it. Below are six common prostate cancer myths along with research-based information from scientists at Fred Hutchinson Cancer Research Center to help men separate fact from fiction.
Myth 1 -- Eating tomato-based products such as ketchup and red pasta sauce prevents prostate cancer. "The vast majority of studies show no association," said Alan Kristal, Dr.Ph., associate director of the Hutchinson Center's Cancer Prevention Program and a national expert in prostate cancer prevention. Kristal and colleagues last year published results of the largest study to date that aimed to determine whether foods that contain lycopene -- the nutrient that puts the red in tomatoes -- actually protect against prostate cancer.
After examining blood levels of lycopene in nearly 3,500 men nationwide they found no association. "Scientists and the public should understand that early studies supporting an association of dietary lycopene with reduced prostate cancer risk have not been replicated in studies using serum biomarkers of lycopene intake," the authors reported in Cancer Epidemiology, Biomarkers & Prevention. "Recommendations of professional societies to the public should be modified to reflect the likelihood that increasing lycopene intake will not affect prostate cancer risk."
Myth 2 -- High testosterone levels increase the risk of prostate cancer. "This is a lovely hypothesis based on a very simplistic understanding of testosterone metabolism and its effect on prostate cancer. It is simply wrong," Kristal said. Unlike estrogen and breast cancer, where there is a very strong relationship, testosterone levels have no association with prostate cancer risk, he said. A study published in 2008 in the Journal of the National Cancer Institute, which combined data from 18 large studies, found no association between blood testosterone concentration and prostate cancer risk, and more recent studies have confirmed this conclusion.
Myth 3 -- Fish oil (omega-3 fatty acids) decrease prostate cancer risk. "This sounds reasonable, based on an association of inflammation with prostate cancer and the anti-inflammatory effects of omega-3 fatty acids," Kristal said. However, two large, well-designed studies -- including one led by Kristal that was published last year in the American Journal of Epidemiology -- have shown that high blood levels of omega-3 fatty acids increase the odds of developing high-risk prostate cancer.
Analyzing data from a nationwide study of nearly 3,500 men, they found that those with the highest blood percentages of docosahexaenoic acid, or DHA, an inflammation-lowering omega-3 fatty acid commonly found in fatty fish, have two-and-a-half times the risk of developing aggressive, high-grade prostate cancer compared to men with the lowest DHA levels. "This very sobering finding suggests that our understanding of the effects of omega-3 fatty acids is incomplete," Kristal said.
Myth 4 -- Dietary supplements can prevent prostate cancer. Several large, randomized trials that have looked at the impact of dietary supplements on the risk of various cancers, including prostate, have shown either no effect or, much more troubling, they have shown significantly increased risk. "The more we look at the effects of taking supplements, the more hazardous they appear when it comes to cancer risk," Kristal said. For example, the Selenium and Vitamin E Cancer Prevention Trial (SELECT), the largest prostate cancer prevention study to date, was stopped early because it found neither selenium nor vitamin E supplements alone or combined reduced the risk of prostate cancer. A SELECT follow-up study published last year in JAMA found that vitamin E actually increased the risk of prostate cancer among healthy men. The Hutchinson Center oversaw statistical analysis for the study, which involved nearly 35,000 men in the U.S., Canada and Puerto Rico.
Myth 5 -- We don't know which prostate cancers detected by PSA (prostate-specific antigen) screening need to be treated and which ones can be left alone. "Actually, we have a very good sense of which cancers have a very low risk of progression and which ones are highly likely to spread if left untreated," said biostatistician Ruth Etzioni, Ph.D., a member of the Hutchinson Center's Public Health Sciences Division.
In addition to blood levels of PSA, indicators of aggressive disease include tumor volume (the number of biopsy samples that contain cancer) and Gleason score (predicting the aggressiveness of cancer by how the biopsy samples look under a microscope). Gleason scores range from 2-5 (low risk) and 6-7 (medium risk) to 8-10 (high risk).
"Men with a low PSA level, a biopsy Gleason score of 6 or lower and very few biopsy samples with cancer are generally considered to be very low risk," Etzioni said. Such newly diagnosed men increasingly are being offered active surveillance -- a watchful waiting approach -- rather than therapy for their disease, particularly if they are older or have a short life expectancy.
"The chance that these men will die of their disease if they are not treated is very low, around 3 percent," she said. Similarly, such men who opt for treatment have a mortality rate of about 2 percent. "For the majority of newly diagnosed cases of prostate cancer, giving initial clinical and biopsy information, we can get a very good idea of who should be treated and who is likely to benefit from deferring treatment."
Myth 6 -- Only one in 50 men diagnosed with PSA screening benefits from treatment. "This number, which was released as a preliminary result from the European Randomized Study of Prostate Cancer Screening, is simply incorrect," Etzioni said. "It suggests a very unfavorable harm-benefit ratio for PSA screening. It implies that for every man whose life is saved by PSA screening, almost 50 are overdiagnosed and overtreated."
"Overdiagnosis" is diagnosing a disease that will never cause symptoms or death in the patient's lifetime. "Overtreatment" is treating a disease that will never progress to become symptomatic or life-threatening.
The 50-to-one ratio is based on short-term follow-up and "grossly underestimates" the lives likely to be saved by screening over the long term and overestimates the number who are overdiagnosed. "The correct ratio of men diagnosed with PSA testing who are overdiagnosed and overtreated versus men whose lives are saved by treatment long term is more likely to be 10 to one," she said.