One month after Joann Bates' mother died of ovarian cancer, the retired school secretary from East San Diego enrolled in an ultrasound screening program designed to detect the deadly cancer.

Screened three times, she felt confident she was healthy. But on the fourth examination, her doctor detected an early-stage tumor.

Bates, 60, was lucky; her tumor was detected promptly. Her mother's tumor had been diagnosed at an advanced stage and it had killed the 80-year-old woman within four months.

By the time ovarian cancer is detected in most women, it is usually too late. More than two-thirds of ovarian cancer patients have widespread cancer at the time of their diagnosis. Despite advances in battling other cancers, the five-year survival rate for ovarian cancer has not significantly changed in two decades--only 38% survive.

To the frustration of doctors and patients, there has been no reliable screening test that can detect early-stage ovarian cancer.

Experts agree that doctors conducting a physical examination are unlikely to find a tumor until it's advanced. And the existing blood test, called a CA-125, which detects elevated levels of a cancer cell byproduct, misses about half of all early-stage malignancies, doctors say.

As experts search for screening-test alternatives, one promising option has emerged: transvaginal ultrasound, or an internal vaginal probe. Federal health officials say this technology is so promising that a nationwide study will be launched next year.

At UC San Diego and other facilities where ultrasound testing is occurring, proponents say the technology could revolutionize diagnostic medicine, doing for ovarian cancer what the mammogram did for breast cancer and the Pap smear did for cervical cancer.

"Ultimately, ultrasound is going to mean early diagnosis of ovarian cancer and therefore improved treatment," said Dr. Barbara Gosink, a UCSD professor of radiology and a driving force in the screening program here. "Women will live longer and we will pick up ovarian cancers earlier."

Other experts agree that it is an auspicious prospect for a diagnostic tool, particularly as one of several that would be used to test for the deadly cancer.

"Clearly, it's the most exciting breakthrough in ovarian cancer diagnosis we've had. It's much more sensitive than blood tests and pelvic exams," said Dr. Arthur Fleischer, chief of diagnostic sonography at Vanderbilt University.