Better Screening for Breast Cancer
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.”
The value of screening for breast cancers in women under the age of 50 has been widely debated, at least as far as mammography is concerned. There is little evidence that mammography is effective at reducing mortality rates for this age group. Meanwhile, health experts worry about unnecessarily exposing women to the risks of radiation. Despite this controversy, the National Cancer Institute recommends that women begin having annual or biennial mammography screenings starting at the age of 40, making Z-Tech’s system an appealing option for some.
A Canadian study published last week in the New England Journal of Medicine found that women with highly dense breasts had a fivefold increase in breast-cancer risk. The study compared the mammogram results of 1,100 women over the course of eight years. Contributing to the risk is the fact that dense tissue and tumors both show up on mammograms as white areas, making it difficult to detect problems. Fat, on the other hand, appears dark and contrasts well with tumors.
“In a breast on a younger person, there’s a lot more fibers and glandular tissue and less fat,” says James Craft, a radiologist at the Medical College of Georgia, which was involved early on in Z-Tech’s study but was not privy to the latest data.
It’s for this reason that Nakashige believes Z-Tech has a chance of dethroning mammography as a screening tool, at least for this higher-risk population for which radiation is a concern and mammography is less effective.
Measuring electrical impedance in tissue is not a new field, but its application to breast-cancer screening only began to emerge as a research area in the early 1990s. That’s when Z-Tech founder Leslie Organ, then a visiting professor at the University of South Carolina, began to study the effects of electric current on malignant tissue.
Mirabel Medical [formerly TranScan], of Austin, TX, also began impedance research in the early 1990s. It is the first and only company to get Food and Drug Administration (FDA) approval to use electrical-impedance screening, but its system is limited to being an adjunct to mammography. Mirabel is currently testing a newer version of its system in a large multisite trial with the U.S. Army. The goal is to get FDA approval as a stand-alone screening tool.
Z-Tech is heading in the same direction. It plans to launch a screening product in Asia and Europe this and in Canada in 2008. A trial is in the works to achieve premarket approval in the United States.
Karina Bukhanov, head of breast imaging at Toronto’s Mount Sinai Hospital, a participant in the trial, is encouraged by Z-Tech’s impedance system but is equally cautious. “We need more studies,” she says. “Right now the numbers aren’t big enough to say with confidence that the sensitivity approaches that of mammography. It could, however, play a more critical role in remote areas where patients don’t have access to mammography.”
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