NEW YORK -- If you're like many men these days, you know that prostate cancer is your No. 2 cancer killer behind lung cancer.

So, your doctor should routinely check your blood prostate specific antigen, or PSA. A high PSA number can indicate cancer.

Prostate patient Dr. Albert Medwid is a surgical oncologist who knows that when your PSA level goes up, as his did, the next step is usually a biopsy. But he did something different.

"Four days after that test, I had a repeat test, and at that time, the PSA decreased by two points. And then five weeks after that test, I had another PSA, and again that PSA decreased again," he said.

Experts say what happened to Medwid is not all that unusual. According to a study in Wednesday's issue of the Journal of the American Medical Association, PSA levels can vary by as much as 30 percent day to day.

"If suddenly you have an abnormal value that's different than it was before, go in and have it rechecked," said Dr. Peter Scardino of Memorial Sloan-Kettering Medical Center in New York. "Maybe wait a month to a month and a half, have it rechecked, make sure it's really up before you act on it."

In other words, you don't have to rush into a biopsy just because your PSA is elevated, unless there are other warning signs, such as:

Your doctor feels something abnormal when he examines your prostate,
You have a family history of prostate cancer, or
You are African-American, a group struck especially hard by prostate cancer.

But is it safe to put off a biopsy?

"Prostate cancer really is one of the most slow-growing cancers," Scardino said. "We think it takes two to four years for it to double in size, so waiting a few weeks, even a few months is not going to change the chances of cure if you really do have a cancer."

This report does not mean you should ignore a high PSA; however, there's so much normal variability in PSA readings, and so many things can cause it to rise, that you should retest over a period of time before you rush into a biopsy, unless there are other warning signs.