WASHINGTON (AP) - A major study finds that a rising PSA level isn't such a good predictor of prostate cancer after all and can lead to many unnecessary biopsies.

Most men over 50 get PSA blood tests. Too much PSA, or prostate-specific antigen, only sometimes signals prostate cancer is brewing. But it can also mean a benign enlarged prostate or an infection.

The screening often detects small tumors that will prove too slow-growing to be deadly. But there's no sure way to tell in advance who needs aggressive therapy.

On the other hand, some men have cancer despite a "normal" PSA count of 4 or below.

Researchers at Memorial Sloan-Kettering Cancer Center found that an increase in the PSA number of otherwise low-risk men isn't useful in determining whether biopsies are needed.

The study tracked 5,519 men who'd taken part in a huge prostate cancer prevention study who all received a biopsy. It's published in the Journal of the National Cancer Institute.