ORLANDO — When a man's first PSA screening test for prostate cancer reveals a very low level, he most likely will not need annual testing, according to research presented at the 38th annual meeting of the American Society of Clinical Oncology (ASCO) in Orlando, Fla.

Currently, most health groups recommend yearly PSA testing for all men 50 and older. PSA, or prostate specific antigen, is a protein produced by the prostate gland.

"About 99% of men with very low or extremely low PSA levels can safely be tested less often than yearly," said lead author E. David Crawford, MD, senior associate director at the University of Colorado's Health Sciences Center in Denver.

If men with PSA levels under one were tested only every five years, and men with PSA levels between one and two were tested every two years, the number of PSA tests every year would drop by more than half, said Crawford.

That could save the US health care system between $500 million and $1 billion yearly. Fewer than 2% of men might have a PSA rise to the abnormal range between tests in such a schedule, said Crawford.

The screening test measures the amount of PSA in a small sample of the patient's blood. Levels below four nanograms (ng) per milliliter (ml) are considered normal. Above that level, doctors may suggest a biopsy to check for signs of prostate cancer.

Some health organizations recommend yearly PSA testing for all men beginning at a certain age, while others do not believe the test has been proven to save lives.

The American Cancer Society (ACS) recommends doctors yearly offer the option of PSA testing to men beginning at age 50, and to African-American men and others at high risk for the disease at 45.

The ACS suggests that men fully discuss with their doctors the potential benefits and risks of early prostate cancer detection and treatment, so they can make informed decisions about testing.

Crawford and colleagues examined data from 27,863 men ages 55 through 74 as part of the PLCO (prostate, lung, colorectal, and ovarian) cancer screening trial. More than 90% of the men had PSA levels in the normal range (less than 4 ng/ml) at the trial start.

A statistical model applied to the men's data predicted that more than 98% of men with PSA under one at the first test would remain in the normal range in the next four years. These men could safely be tested every five years.

The model showed that more than 98% of those with levels between one and two would still be in the normal range during the next year, so could safely test every other year.

"Very clearly, because of the very large size of this study, nearly 28,000 men, and because of its careful follow-up, this is a very important study," said Harmon Eyre, MD, vice-president for medical affairs and research at the ACS.

Eyre said it's too early to say how all experts will regard the data and recommendations.

But he noted that the ACS scientific advisory committee that reviews new findings on a yearly basis will examine the study data and its conclusions to determine whether ACS will modify its guidelines.

Because the potential savings, if verified, could be used for other, needed health care, such a consideration is very important, Eyre noted.

If verified, the findings that many men could safely be tested less often could be very reassuring to men, he noted.

"Very often, any test that can be done less often than annually is generally very welcomed by the population," Eyre said.