New data should help reduce incidence of low-grade tumors, experts say
MONDAY, Sept. 24 (HealthDay News) -- Prostate cancer prevention studies conducted since the 1990s are poised to revolutionize the field in the next five years, a Canadian analysis concludes.
"I am optimistic that for the coming generation, beginning with men in their 20s and 30s, we will have a viable strategy to decrease the chance of developing prostate cancer later in life," said study lead author Dr. Neil Fleshner.
A professor of surgery, Fleshner heads the division of urology at Princess Margaret Hospital, part of the University Health Network at the University of Toronto.
His team's overview of the last 15 years of prostate cancer prevention research is published in the Nov. 1 issue of Cancer.
According to the U.S. National Cancer Institute (NCI), cancer of the prostate is the most common non-skin cancer among American men. Most patients diagnosed with the disease do not ultimately die of it. However, because of its high prevalence, prostate cancer remains the third biggest cancer killer for men in the Western world.
By age 40, one-third of men have already developed small carcinomas of the prostate, the researchers noted. By age 60, that figure rises to 60 percent, and, in North America, one in seven men will develop prostate cancer at some point in their lives.
But the disease is also often slow-moving, sometimes taking decades to develop from a single prostate cancer cell to advanced-stage illness.
That fact has led to the hope that doctors could intervene in ways that could halt disease progression at an early stage.
One such study reviewed by Fleshner and his colleagues was the Prostate Cancer Prevention Trial (PCPT), overseen by the NCI.
In this instance, NCI researchers looked at the ability of finasteride -- a so-called 5-alpha reductase inhibitor (5ARI) medication -- to impede the growth-promoting impact of hormones such as testosterone on prostate cancer.
Designed to interfere with the body's ability to uptake testosterone and other male hormones, finasteride was offered to half the almost 19,000 men over the age of 55 who participated in the seven-year study.
At the study's start, all the men screened as "normal" following digital rectal exams. As well, all had registered low-scoring prostate-specific antigen (PSA) levels. An elevated level of PSA in the blood is an indication of prostate cancer.
Yearly digital rectal exams and PSA screenings revealed that almost 25 percent of the men on placebo went on to develop prostate cancer. However, just a little over 18 percent of those taking finasteride got the disease.
Fleshner and his associates noted, however, that most of the cancer cases prevented appeared to be of the early stage, low-grade variety. More serious, higher-grade disease actually appeared to become more common among patients taking finasteride. This raises concern that the medication might actually hasten disease progression, the Canadian group cautioned.
Nevertheless, their review concluded that finasteride might, in the near future, become an effective prevention tool for men with a strong family history of the disease.
Additional studies are currently under way to explore the benefits of newer hormone manipulation drugs, they noted, including the 5ARI drug dutasteride and the selective estrogen receptor modifier toremifene. Results should be available in a few years.
Meanwhile, the Canadian team also uncovered evidence suggesting that limiting fat in the diet might also reduce prostate cancer risk. Various studies have highlighted unhealthful connections between fat and pesticide exposure, testosterone level increases, and the rise of oxidative stress -- all of which seem to contribute to prostate disease risk.
By contrast, evidence has mounted that increasing vitamin E and selenium intake could also protect against prostate cancer, they said. Recent research also suggests that consuming more green tea, soy, vitamin D, and lycopene (typically found in tomatoes) might confer similar benefits.
Fleshner and his colleagues hailed the new emphasis on prevention. The arrival of even more helpful prevention information might be just around the corner, they said.
"What's exciting now is that there's no doubt any longer that prostate disease is preventable," said Fleshner. "This will not necessarily translate into improved mortality rates, because it may be that we will be able to prevent more low-grade disease than high-grade."
But many men with low-grade disease currently undergo surgery and other treatments that can impact their quality of life, he noted. "So, even if we are able to reduce just the need for unnecessary treatment, this will be a good step," Fleshner said.
Not everyone shares that optimism, however.
Dr. Nelson Neal Stone, a clinical professor of urology and radiation oncology at the Mount Sinai School of Medicine in New York City, believes that when it comes to preventing prostate cancer, "we're still sort of at a loss."
"Today, you can't really advise a patient to do anything to prevent prostate cancer," he said. "The best study so far -- the PCPT study-- did show a 25 percent drop in prostate cancer, but that was in low-grade tumors, whereas the incidence of high-grade tumors may actually have gone up. And a lot of the dietary factors that showed promise --vitamins, selenium -- have come into question as to whether they're really helping patients."
"So, I would agree that in five year's time, we will probably come up with strategies to reduce the clinical incidence of the disease in terms of detecting low-grade cancer," he added. "But that doesn't have much meaning in a patient's life. What has meaning is the ability to prevent a high-grade tumor from metastasizing and potentially ending a patient's life. And nobody has shown that anything can reduce that."
"In my opinion, the best strategy we have now is early detection," Stone said. "If you find a patient with an aggressive prostate cancer, and it's small and in the prostate and you find it early, you save that patient's life."
For more on prostate cancer prevention, visit the U.S. National Cancer Institute.
SOURCES: Neil Fleshner, M.D., head, division of urology, Princess Margaret Hospital, University Health Network, University of Toronto, Ontario, Canada; Nelson Neal Stone, M.D., clinical professor, urology and radiation oncology, Mount Sinai School of Medicine, New York City; Nov. 1, 2007, Cancer
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