Test for Prostate Cancer Cuts Deaths by 69%, Study Finds
Routine screening for prostate cancer with a controversial test called PSA can reduce the number of deaths from the disease by 69% and has the potential to save more than 27,000 lives in the United States each year, Canadian researchers reported Monday.
Such screening catches tumors at an early stage when they can be treated much more effectively, Dr. Fernand Labrie of Laval University in Quebec said at a Los Angeles meeting of the American Society for Clinical Oncology.
This is the first major study of the effectiveness of the test, which measures levels of a protein called prostate-specific antigen (PSA) that is released into the blood by tumors.
“If the screening is started, as suggested by the American Cancer Society and by us, at the age of 50, diagnosis of metastatic prostate cancer should practically disappear,” Labrie said.
PSA screening been available for more than a decade, and both the American Cancer Society and the American Urological Assn. recommend yearly tests for men over 50. But many physicians do not order it for their patients because there has been no proof that it prevents deaths.
Critics also note that there are a significant number of false positives associated with the PSA tests--abnormally high values that are subsequently found to be caused by noncancerous growths. Such results can produce great anxiety for two or three weeks while physicians try to confirm the initial results. Widespread use of the test will thus subject a large number of men to such unnecessary stress, they charge.
But the new study may change some minds. “Simply put, screening saves lives,” Labrie said.
Not Everyone Is Convinced
Others disagreed, however. “The study is extremely provocative, but it is certainly not conclusive,” said Dr. Thomas E. Finucane of the Johns Hopkins School of Medicine, a longtime critic of the test.
“This is encouraging research, but it needs to be confirmed,” said Dr. Derek Raghavan of USC’s Norris Comprehensive Cancer Center. “It would be premature to set national guidelines based on any one study, especially as routine implementation of screening asymptomatic patients will be very expensive to the general community.”
Labrie noted, however, that the cost per life saved would be comparable to that for mammography.
About 184,500 new cases of prostate cancer are diagnosed each year in the United States, with about 39,000 deaths. It is the second-leading cause of cancer deaths in men, after lung cancer. But it is almost 100% curable if it can be caught at an early stage, before it has spread.
The problem is that there are two distinct variants of prostate cancer, Raghavan said. One is a “vicious killer” that can spread rapidly throughout the body, while the second is an essentially benign tumor that accompanies aging.
As many as 9.5 million American men have the latter form without knowing it, Finucane noted. And surgery, which carries its own risks, can be more dangerous than simply ignoring it. In elderly patients, physicians often choose not to treat such slow-growing tumors because the patient is likely to die from some other cause before the tumor becomes a threat. Both forms of the cancer secrete PSA.
Labrie, who pioneered the use of hormone-blocking drugs in advanced prostate cancer, began the study in 1988, before use of PSA began to spread. His team randomly divided the 46,193 Quebec men between the ages of 45 and 80 into two groups and invited half to have the screening.
Stark Difference in Statistics
In the eight years of follow-up, there were five deaths in the 8,129 men who came in for screening, compared to 137 deaths among the 38,160 men who were not screened. That works out to a 69% decrease in deaths among those who were screened.
Of the five deaths in the screened group, he added, prostate cancer was detected in the first exams of four of the men--suggesting that they already had advanced cancer when they entered the study.
Labrie noted that the death rate from prostate cancer in Canada is virtually the same as that in the United States, so that the results can be extrapolated to this country.
Critics are concerned, however, that less than a quarter of those invited to be screened actually enrolled in the study. That opens the possibility of a “selective bias,” Finucane said. Men who already knew they had prostate cancer, for example, might not have selected screening, while those who are very health conscious and at low risk of the disease may have enrolled.
“That’s a big worry,” he said.
The study is thus not likely to provide the final word on an issue that has dramatically divided the medical community. To illustrate that division, Finucane noted that none of the male physicians in the division of geriatric medicine at Johns Hopkins have had a PSA test, while all of those in the urology division have. “There is a fundamental difference in understanding of the data,” he said.
