Computer double-checks mammograms.

Even a trained radiologist can miss a potential malignancy when reading a mammogram, the specialized diagnostic X ray aimed at locating incipient breast tumors. In fact, physicians can fail to spot between 10 and 30 percent of cancers present in women who get breast X rays.

With the help of a new computer system, though, physicians may cut the number of missed cancer diagnoses in half.

Kunio Doi, a radiology researcher at the University of Chicago, and his colleagues report putting the first computer-assisted program for analyzing mammograms into clinical use. Doi likens the system to a spell-checking program, used in word processing to catch typographical errors before printing a document. The computer mammography program offers a second opinion, pointing out areas that should be double-checked before signing off on a patient's good health.

In retrospect, physicians find that as many as two-thirds of all false negative mammograms show subtle evidence of cancer that interpreters overlooked, Doi's team reports.

In roughly half of all early breast cancers, tiny deposits of calcium resembling a "constellation of faint stars" appear on the mammogram. Often, other features on the X ray obscure those starlike deposits. Doi's group has trained the computer to spot the calcified constellations, even when covered by "clouds" of normal tissue, they explain.

By comparing the symmetry of the right and left breasts, the system can detect subtle masses, which account for another 40 percent of early cancers.

Three studies give the computer detection system a good grade, the scientists state. The first found the computer catching 85 to 90 percent of early cancers in 200 mammograms. The second showed the system spotting half the tumors missed by trained radiologists. The third noted that a radiologist using the computer found 92 percent of the cancers, compared to 85 percent for a radiologist working alone.

The computer and physician, each with distinct strengths and weaknesses, complement each other, says Robert Schmidt, a Chicago radiologist. Physicians make the best final judgments, but the computer doesn't get distracted by interruptions or feel tired and cranky.

The computer isn't perfect, Schmidt adds, but it can substantially improve diagnostic accuracy.

The researchers estimate that the system will cost about $100,000, making it affordable to most radiology groups.

As many as one U.S. woman in eight will have breast cancer during her lifetime, according to the American Cancer Society. In 1995, that will amount to roughly 207,000 new cases.