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WEDNESDAY, Aug. 14 (HealthDay News) -- The aggressiveness of prostate cancer doesn't appear to change over time, according to a new study that bolsters the argument for "watching and waiting" in cases of low-grade tumors.
When prostate cancer is diagnosed, a measure called the Gleason score helps predict the aggressiveness of the disease. But whether low-risk cancer turns into high-risk cancer over time wasn't clear, the researchers said. This new study, published Aug. 15 in Cancer Research, suggests it does not.
In the last 22 years widespread prostate-specific antigen (PSA) screening has led to more prostate cancer diagnoses, but "the proportion of high Gleason score disease did not change drastically," said lead researcher Kathryn Penney, an instructor in medicine at Harvard Medical School in Boston. "This suggests that Gleason does not progress to a higher grade over time," she said.
Therefore, men whose cancer has a low Gleason score may want to opt for active surveillance rather than surgery to remove the prostate or radiation therapy, Penney said.
The Gleason score is based on a microscopic analysis of tissue removed during a biopsy. Grading the severity, aggressiveness and stage of a prostate tumor helps doctors determine a patient's prognosis.
"The finding that Gleason score progression is uncommon may help men feel more comfortable choosing active surveillance," Penney said.
One expert said the study has the potential to influence current practice.
"This study should have a major impact on how we treat prostate cancer," said Dr. Louis Kavoussi, chairman of urology at North Shore-LIJ's Arthur Smith Institute for Urology in New Hyde Park, N.Y.
"We know prostate cancer is over treated," Kavoussi said. Many patients want treatment, he added.
"But in reality, a great number of patients can be managed with surveillance and have prostate cancer which will never cause them any symptoms or shorten their lives," Kavoussi explained.
"What is needed is a way to identify those patients," Kavoussi said, adding this study might help in that regard.
For the study, Penney's team collected data on 420 men who took part in the well-known Physicians' Health Study and 787 men who were part of the Health Professionals Follow-Up Study. All were diagnosed with prostate cancer between 1982 and 2004 and had their prostate removed.
The researchers divided the data into four groups based on the time of treatment looking for differences before and after screening for PSA became common practice.
The percentage of men who had PSA screening nearly doubled between 1994 and 2000, they found. And the number of late-stage cancers dropped 85 percent from 1982-1993 to 2000-2004 -- from about 20 percent to just 3 percent. Staging refers to how far the cancer has spread.
However, Gleason scores decreased only 30 percent over the same time period.
Further analysis showed that the moderate drop in Gleason scores was not because cancer progression was prevented by screening, but rather because many low-grade cancers were found with PSA screening, the researchers pointed out.
Another expert, Dr. David Samadi, chairman of urology and chief of robotic surgery at Lenox Hill Hospital in New York City, said the decision to treat or not to treat a low-risk prostate cancer has to be decided on an individual basis.
"It's dangerous to say every low-risk prostate cancer should be treated the same," Samadi said.
Gleason scores range from 2 to 10. The higher the score, the greater the likelihood the cancer will spread quickly. But Gleason scores can be subjective, Samadi said. "One pathologist can read the slide and grade it as Gleason 6. Somebody else can look at it as Gleason 7," he said.
If samples from a biopsy show a low Gleason score and the patient also had a low PSA that hasn't changed over several months, then active surveillance is a good option, Samadi suggested.
But someone in his early 50s who has multiple samples with a Gleason score of 6 likely has an aggressive tumor, he added.
"We don't want to send a message that every seemingly low-risk prostate cancer should be treated with active surveillance," Samadi said.
Moreover, active surveillance doesn't mean doing nothing, he pointed out. It means yearly biopsies and regular PSA screenings to look for changes in the cancer.
Also, surgery and radiation treatment have improved, and the risks of side effects such as incontinence and impotence are greatly reduced. "If you remove the prostate and cure them, that's as good as any kind of active surveillance," Samadi said.
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SOURCES: Kathryn Penney, Sc.D., instructor in medicine, Harvard Medical School, Boston; Louis Kavoussi, M.D., chairman, urology, North Shore-LIJ, Arthur Smith Institute for Urology, New Hyde Park, N.Y.; David Samadi, M.D., chairman, urology, and chief, robotic surgery, Lenox Hill Hospital, New York City; Aug. 15, 2013, Cancer Research