Prostate cancer study casts doubt on PSA test reliability

Malignant cells are found despite `normal' readings

May 27, 2004|By NEW YORK TIMES NEWS SERVICE

Significant numbers of older men whose results on a popular screening test for prostate cancer are normal might nonetheless have cancer, a new study has found.

The result, medical experts say, raises questions about what a "normal" test score should be and whether these men are better off left alone or treated when, through biopsies, cancer cells are discovered.

It also amplifies a controversy over the test, known as the PSA, and whether finding prostate cancer early and treating it by removing or destroying the prostate is, on balance, helping or harming men.

The PSA test is a blood test that looks for prostate specific antigen, a protein released by prostate cells. When the prostate gland enlarges, whether because of cancer or benign conditions, PSA levels in the blood tend to rise.

The test was initially used to look for recurrences of cancer after men had been treated. But in the 1990s it came into widespread use as a screening test to find new cancers.

In that context, cancer experts informally agreed upon a convention: When a PSA test finds more than 4 nanograms of the protein in a milliliter of blood, doctors usually recommend biopsies to see whether cancer is present.

Needles are inserted into the prostate to withdraw cells for analysis. When a biopsy finds cancer, almost all men opt for treatment, usually surgery or radiation to destroy the prostate gland.

But the new study, being published today in The New England Journal of Medicine, reports that as many as 15 percent of men with PSA levels less than 4 had cancer when their prostates were assessed with biopsies.

Never risk-free

While higher PSA levels confer greater risk, there appears to be no level at which there is no risk of prostate cancer, said the lead investigator, Dr. Ian M. Thompson, chief of urology at the University of Texas Health Science Center in San Antonio.

Dr. Howard Parnes, who directs prostate cancer research at the National Cancer Institute's division of cancer prevention, responded to the study by saying: "Now we don't have a clear definition of normal and abnormal. Before these data were out, we were comfortable with the notion that 4 is a cutoff between normal and abnormal. Now these data very clearly tell us that 4 is not a cutoff."

But the study, which involved 2,940 men ages 62 to 91, was not designed to show what cutoff should be used for PSA levels. And there are no easy answers about whether a man with a low PSA level should have a biopsy, said Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society.

Cancers in such men are microscopic - a doctor cannot feel them - and there are no symptoms. The biopsy decision could depend on how old the man is, his family history or how frightened he is of prostate cancer.

"These are decisions that are going to have to be discussed between people and their health care providers," Lichtenfeld said.

Parnes worries that men with low PSA levels and their doctors will see the study results and decide unequivocally that the safest thing to do is have a biopsy.

Huge numbers

In that case, because about 90 percent of men have levels that are below 4, huge numbers would have biopsies, huge numbers would be told they have cancer, and huge numbers might opt for treatment that is perhaps unnecessary.

Prostate cancer is exceedingly common; autopsy studies in which prostates are examined section by section find microscopic cancerous cells in most elderly men. But it tends to smolder silently, never spreading or causing problems in a man's lifetime.

Still, it can be deadly. Prostate cancer kills 30,000 American men a year. As yet, there is no way to know for sure whether a cancer will spread and kill, so most men choose treatment although it can lead to impotence or incontinence.

`Don't know what to do'

Some physicians, such as Dr. H. Ballentine Carter, a professor of urology and oncology at Johns Hopkins University, urge caution about biopsying men with PSA levels below 4.

"We will find a lot of cancer, and we will not know what to do about it," he said. "That is very worrisome."

"The reason for caution," Carter said, "is because right now we don't have the ability to know who in this low PSA range has a cancer that is likely to be harmful.

"There is nothing wrong with doing a PSA, but we don't need to act on it immediately. We have an out here: We can follow men over time, and biopsy those whose PSA goes up."

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