New Blood Analysis More Sensitive : Better Test for Prostate Cancer Found

A new blood test that could help diagnose and monitor the treatment of prostate cancer appears to be much more sensitive than a commonly used existing method.

“This is infinitely more sensitive and will, in my view, undoubtedly replace the existing test,” said Dr. Thomas A. Stamey of the Stanford University School of Medicine.

There are about 96,000 new cases of prostate cancer and 27,000 deaths from the disease each year in the United States, making it the third leading cause of cancer and cancer deaths in men.

If the prostate gland is found to contain cancer, it is usually removed surgically and patients are given radiation treatments to kill any remaining cancer cells in their bodies.

Doctors monitor the success of the treatment and check for any recurrences by measuring the level of an enzyme in the blood known as prostatic acid phosphatase or PAP, which is secreted by prostate cells.

Different Enzyme Measured

Stamey and his colleagues compared that test to another that measures a different enzyme secreted by the prostate known as prostate-specific antigen or PSA.

The researchers measured the levels of the two enzymes in blood samples from 699 patients, 378 of whom had prostate cancer.

The PSA level was elevated in 122 of 127 patients with newly diagnosed, untreated prostate cancer, including seven of 12 who had unsuspected early cases and all of 115 with more advanced cases.

The PSA level increased as the disease progressed and was proportional to the size of the tumor.

In contrast, PAP levels were elevated in only 57 of the patients with cancer.

Check for Recurrences

More importantly, in six patients who underwent surgery and then were followed up with tests measuring the enzyme levels in their blood, PSA but not PAP measurements appeared useful for detecting residual and early recurrences of cancer.

“We conclude that PSA is more sensitive than PAP in the detection of prostatic cancer and will probably be more useful in monitoring responses and recurrence after therapy,” Stamey and his colleagues said in reporting their results in a recent issue of The New England Journal of Medicine.

Stamey cautioned, however, that the test could not be used for routine screening because it often produces false positive results in patients suffering from a non-cancerous and common inflammation of the prostate.

Based on the findings, the researchers recommended prostate cancer patients have their PSA levels measured three weeks after having their prostate removed and then periodically after that to check for recurrences.

‘Much Better Marker’

“It will give us a much better marker of the patients’ progress,” said Stamey in a telephone interview. “We’re hoping we can cure more patients with this technique.”

In two patients in the study, PSA levels became detectable nine and 12 months after their prostate had been removed. No cancer could be found through standard detection methods, but the PSA dropped back down to zero after the pelvic area was irradiated.

Dr. Ruben F. Gittes of the Scripps Clinic and Research Foundation in La Jolla, Calif., in an editorial accompanying the study, said the findings offer strong evidence of the usefulness of the new test.

“It seems likely to replace the ‘veteran’ PAP assay in the staging and follow-up of all cases of prostatic cancer,” he said. Staging is a process in which the progress of the cancer is measured.