Watching how quickly PSA levels rise in prostate cancer patients over the years can help doctors avoid unnecessary surgery, according to a study released Tuesday.

The rate of change in PSA, or the prostate specific antigen test, may predict which tumors are fast-growing and should be treated right away, according to research reported at the American Urological Association meeting in San Francisco. This may eliminate at least 80 percent of unwarranted biopsies that can lead to surgery in men with elevated PSA levels, said Thomas Neville, one of the study researchers.

Ways to make PSA tests more effective are needed to differentiate men with an aggressive form of cancer from those who don’t need immediate treatment, Neville said. While a single test can catch tumors early, it can also lead to false positives that trigger unnecessary tests, biopsies and treatment.

“This is a window into the cancer without doing the biopsy,” said Neville, founder and chief executive of Soar BioDynamics, a closely held San Francisco-based company that provides personal health analysis, in a telephone interview last week. “If it’s a 50 percent growth rate, that’s a real nasty cancer.”

“Working with their doctor, they can analyze that and look for early clues,” Neville said. “They can jump on it now and catch aggressive cancers early in a treatment window that allows for a good chance of success.”

Prostate cancer is the most common malignancy other than skin cancer to occur in U.S. men, and is the second-leading cause of cancer death, behind lung tumors, according to the American Cancer Society. More than 192,280 new cases of prostate cancer occurred in U.S. men last year, killing 27,360, the cancer society said.

The PSA test itself can’t detect cancer. Higher PSA scores can be caused by cancer cells as well as by an enlarged prostate and by infections and inflammation, Neville said.

Men who have elevated PSA tests are often urged to have a biopsy, a procedure that removes tissue from the prostate to look for the presence of cancer cells. The biopsies can be inconclusive in showing whether a patient has cancer cells that are growing fast enough to pose an actual threat, Neville said. Those patients are often urged to get treatment for cancer.

Surgery, radiation, hormone therapy and chemotherapy are common procedures for prostate cancer. Treatment may be painful and sometimes leads to lifelong urinary incontinence and impotence.