A new device that screens for breast cancer by measuring electrical resistance in tissue could soon become a painless, radiation-free, and less costly alternative to mammography for women at high risk for the disease.

The company developing the technology, Z-Tech, based in Westford, MA, recently completed international trials of screening methods on 3,500 subjects at 28 different sites. A paper detailing the outcome of the two-year trial will be submitted later this year for peer review, the company says. But preliminary results indicate that the device catches more cancers and has fewer false positives than film mammography, most notably in patients younger than 50 years of age.

Steven Nakashige, chief executive officer of Z-Tech, says the company's test works best on women with dense breast tissue, an area where mammography is generally at its weakest. The test also takes only a few minutes and doesn't require a specially trained technician. Its simplicity, as well as the fact that it doesn't emit the potentially harmful ionizing radiation associated with mammography x-rays, could make it an effective tool in battling this deadly and most frequently diagnosed cancer in women. "We believe this would significantly increase [screening] compliance rates, which would help detect cancers earlier," says Nakashige. "And if you detect cancers earlier, you can reduce mortality rates."

Some observers say that Z-Tech's technology, while an improvement over mammography, needs to perform dramatically better if the aim is to encourage regular screening of the population at an earlier age. The worry is that false positives, even when there are fewer compared with mammography, would increase on an absolute basis. "You're implementing something that's guaranteed to produce X number of false alarms," says Alexander Hartov, an expert on the medical applications of electrical impedance at the Thayer School of Engineering at Dartmouth College, in Hanover, NH. "What are the repercussions in terms of public-health cost? Is it worth doing?"

So-called electrical-impedance scanning also faces competition from a variety of other emerging screening technologies that use everything from low-level microwaves to infrared light to locate breast tumors. The challenge with using impedance measurements, says Hartov, is to make it sophisticated enough so that it can distinguish between cancers and less serious abnormalities--a complex computational task that Dartmouth engineers are tackling.

The Z-Tech system works on two principles: that malignant tumors permit electricity to pass through more easily than noncancerous cells do, and that the left and right breasts of a healthy woman typically exhibit the same electrical characteristics. A disposable flower-petal-shaped disc is attached to each breast. Each of the 12 petals on the disc is an electrode, which bends over the contour of the breast and sticks to the skin with a light adhesive. A mild current is then applied between the electrodes in more than 300 combinations, and the data is sent to a bedside computer for immediate analysis.

"Our device compares one breast to the other breast and looks for the breast that has the higher [electrical] impedance," explains Nakashige. "It uses an algorithm and determines if the impedance exceeds a certain threshold. If it does, there's a high probability it's cancerous." He emphasizes, however, that the test doesn't produce an image of the breast and can't detect tumor types. "Our device is really a screening device. It's more of a yes-no answer that you get. You just want to determine whether someone should go on for diagnostic [mammography, ultrasound, or MRI] testing or go home."