SEATTLE – 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.
This article was first published at www.newswise.com