Prostate cancer: six prevailing myths

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Here are six common prostate cancer myths, along with research-based information from US scientists at Fred Hutchinson Cancer Research Centre to help men separate fact from fiction.

Myth 1

Eating tomato-based products such as tomato sauce and red pasta sauce prevents prostate cancer.

"The majority of studies show no association," says Dr Alan Kristal, associate director of the centre's Cancer Prevention Programme and a national expert in prostate cancer prevention.

Kristal and his colleagues have published results of the largest study undertaken to date that aimed to determine whether foods that contain lycopene - the nutrient that puts the red in tomatoes - actually protects 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 the journal, Cancer Epidemiology, Biomarkers & Prevention last year.

"Recommendations of professional societies to the public should be modified to reflect the likelihood that increasing the intake of lycopene 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 says.

Unlike oestrogen and breast cancer, where there is a very strong relationship, testosterone levels have no association with prostate cancer risk, he says.

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.

Myth 3

Fish oil (omega-3 fatty acids) decreases the risk of prostate cancer.

"This sounds reasonable, based on an association of inflammation with prostate cancer and the anti-inflammatory effects of omega-3 fatty acids," Kristal says.

However, two large, well-designed studies - including one led by Kristal, and 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.

Analysing 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 with 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 says.

Myth 4

Dietary supplements can prevent prostate cancer.

Several large, random trials that 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 supplements, the more hazardous they appear when it comes to risk," Kristal says.

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 the Journal of the American Medical Association found that vitamin E actually increased the risk of prostate cancer among healthy men.

The Hutchinson Centre oversaw statistical analysis for the study, which involved nearly 35,000 men in the US, Canada and Puerto Rico.

Myth 5

We don't know which prostate cancers detected by screening for PSA (prostate-specific antigen) need to be treated and which 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 they are left untreated," says biostatistician Dr Ruth Etzioni, a member of the centre's Public Health Sciences Division.

In addition to blood levels of PSA, indicators of aggressive disease include tumour volume (the number of biopsy samples that contain cancer) and Gleason score (predicting the aggressiveness of cancer by the look of biopsy samples under a microscope). Gleason scores range from 2 to 5 (low risk), 6 to 7 (medium risk), and 8 to 10 (high risk).

"Men with a low PSA level, a Gleason score of six or lower, and very few biopsy samples with cancer, are generally considered to be very low risk," Etzioni says.

Such newly diagnosed men increasingly are being offered active surveillance - a watch-and-wait 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, about 3%, Etzioni says. Similarly, such men who opt for treatment have a mortality rate of about 2%.

"For the majority of newly diagnosed cases of prostate cancer, given 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 Randomised Study of Prostate Cancer Screening, is simply incorrect," Etzioni says.

"It suggests an unfavourable harm-benefit ratio for PSA screening. It implies that for every man whose life is saved by PSA screening, almost 50 are over-diagnosed and over-treated."

Over-diagnosis is diagnosing a disease that will never cause symptoms or death in the patient's lifetime. Over-treatment means 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, "grossly under-estimates" the lives likely to be saved by screening over the long term, and over-estimates the number who are over-diagnosed.

"The correct ratio of men diagnosed with PSA testing who are over-diagnosed and over-treated, compared with men whose lives are saved by treatment long term, is more likely to be 10 to one," Etzioni says.

Source: Business Day via I-NET Bridge