Traditional screening for cervical cancer-a pap smear followed by microscopic examination of the cervix-often gives false positives that force needless, painful, and costly biopsies. A new optical diagnostic device now being tested in large human trials could give more precise answers cheaply. And it could reach patients in two to three years.

The new technology is a pencil-sized probe that shines ultraviolet and visible light onto the cervix. Precancerous cells contain more mitochondria-the power plants of cells-which fluoresce when light of those wavelengths strikes them; so an increase in fluorescence means more precancerous cells. In a study of more than 100 women last year, researchers at the University of Texas at Austin and the M. D. Anderson Cancer Center in Houston, TX, found the method provided 50 percent fewer false-positive readings than standard methods. Now, two trials involving 1,800 women in Texas and Canada are under way, and the technology could be ready for the U.S. Food and Drug Administration’s approval process next year, says Michele Follen, an oncologist at M. D. Anderson. “Physicians could screen, diagnose, and make decisions about treatment all in one shot,” says Rebecca Richards-Kortum, a biomedical engineer at the University of Texas and one of the probe’s developers. That would be particularly welcome in developing countries, where most of the world’s 300,000 annual cervical-cancer deaths occur, and where today’s testing methods are unavailable or beyond the means of most women. In the U.S., Follen estimates, widespread adoption could save more than $600 million a year in health-care costs.

Other groups are using infrared light to check for breast cancer. At some wavelengths, infrared light can penetrate several centimeters into the body and is sensitive to changes in blood oxygen content and blood volume, which correlate with tumor growth. “In a few years, radiologists are going to be able to press a button and get optical information to complement mammography,” says Bruce Tromberg, a biomedical engineer developing an optical breast-cancer screening test at the University of California, Irvine. Using light also avoids the need for radiation, says Daniel Sullivan, head of the cancer imaging program at the National Cancer Institute in Bethesda, MD. He cautions that optical imaging won’t replace existing methods but could complement them to improve accuracy and reduce needless biopsies.