Doctors now usually focus on the level of prostate-specific antigen measured by the PSA test and recommend follow-up biopsies for men whose levels are four points or higher.
The study showed that the rate at which the PSA level increases during the year before the cancer is diagnosed is nearly ten times better at predicting which tumors are deadly than is the PSA level itself.
"The study is pretty definitive," lead researcher Dr. Anthony D'Amico, a professor of radiation oncology at Harvard Medical School, told the Associated Press. "It's not the level of PSA that matters, it's the change from year to year."
The new study followed 1,095 men, 65 years old on average, who had prostate cancer. The men received PSA screenings at least once a year and underwent prostate surgery between 1989 and 2002.
Twenty-eight percent of the men whose level rose more than two points the year before diagnosis died of prostate cancer within seven years even though they underwent surgery.
Thursday's findings may help determine which prostate cancer patients should consider prostate-removal surgery and which can simply keep close tabs on the cancer. Doctors often recommend "watchful waiting" because the surgery can cause impotence and incontinence, and many prostate tumors are so slow-growing that men eventually die of something else.
Although one man in six will get prostate cancer during his lifetime, the American Cancer Society reports that only one in 32 will die of this disease.
The American Cancer Society currently recommends that most men begin getting PSA tests at age 50. D'Amico said a baseline PSA level should be determined at age 35 to spot changes.
"A man whose PSA is 3.5 may have nothing to worry about if it was 3.49 the year before, but a lot to worry about if PSA last year was 1," D'Amico told Reuters.
PSA levels alone are not always reliable. A recent study found the test missed about 15 percent of prostate cancers in older men whose readings were below the 4.0 point threshold.
Study author Dr. William Catalona of Northwestern University in Chicago said he thought to investigate "PSA velocity" while conducting a previous study of 36,000 men.
"I had some men come in and their PSA would be 0.6 one year, then 1.4 the next, then 2.4, then 3.2. There would be an obvious trend, and I would say 'We can't do a biopsy until the PSA reaches 4'," Catalona told Reuters.
"Then they'd come in and have a PSA of 6," he told the news agency. The men would get immediate surgery to remove their prostates and many times the cancer had already spread.
"Then they'd be really angry," Catalona said.
-- Compiled from wire reports and other media sources
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July 8, 2004, 1:45pm EDT
