More than 90 percent of mammograms in the United States now use computer-aided-detection, or CAD, but a new study by Seattle researchers and others show the high-tech device doesn’t improve cancer detection — and may lead to some missed cases.

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A high-tech tool now used on more than 90 percent of U.S. mammograms doesn’t improve breast-cancer detection and may lead to missed diagnoses — all while adding at least $400 million to the nation’s annual health-care tab, a study by investigators in Boston and Seattle has found.

Computer-aided-detection (CAD) for mammography, which aims to double-check radiologists’ screening results, didn’t improve accuracy by any measure, according to the largest study to date of the controversial tool, published Monday in the journal JAMA Internal Medicine.

“This is a perfect example of something that has taken off without adequate analysis of the harms and benefits,” said Diana S.M. Buist of Seattle’s Group Health Research Institute, which helped conduct the National Cancer Institute-funded study by the Breast Cancer Surveillance Consortium.

An editorial accompanying the study suggests that Congress should stop allowing Medicare to reimburse health-care centers for the procedure, and a University of Washington expert says women may want to demand CAD-free mammograms.

“They should not be required to pay for it,” said Dr. Joann G. Elmore, a UW professor of medicine who has studied CAD and specializes in diagnostic accuracy. She was not involved in this study.

Group Health investigators worked with lead author Dr. Constance Lehman of Massachusetts General Hospital in Boston to analyze more than 625,000 digital mammograms read by 271 radiologists at 66 sites across the United States between 2003 and 2009.

The study, which reviewed mammograms from nearly 324,000 women, found that radiologists detected cancer in about four of every 1,000 women — and invasive cancer in about three of those four — whether they looked at nearly half a million digital mammograms with CAD or nearly 130,000 without it.

Additionally, among 107 radiologists who interpreted mammogram results with and without CAD, the study found they were more likely to miss cancers when they used the computer-aided review. Radiologists’ sensitivity, or the proportion of times they correctly identified cancer, was 83 percent when they used CAD — and nearly 90 percent without it.

“What this shows is that when they used CAD, they did worse,” Buist said, adding that some radiologists may use the device as a crutch.

CAD did detect more noninvasive, stage 0 ductal carcinoma in situ, or DCIS, but finding more DCIS does not necessarily improve eventual outcomes for women, research by the National Institutes of Health and others has shown.

About 39 million mammograms, or X-rays of the breast, are performed in the United States each year, according to the federal Food and Drug Administration (FDA). CAD was approved by the FDA in 1998 and added for reimbursement by the Centers for Medicare and Medicaid Services (CMS) in 2002. Medicare generally pays about $7 for a CAD screening, while private insurers can charge $20 or more.

Within years of the reimbursement ruling, CAD mammography software was installed in breast-screening centers across the country. CAD now comes standard on most mammogram machines, despite more than a decade of sharp debate about how well the device works. The notion that a computer review could only improve detection was too hard to resist, Buist said.

“The bad-news story from society’s perspective is we’re spending a lot of money on something that sounded like a great idea — and just isn’t,” she said.

The new, well-designed study may help settle years of debate, said Dr. Debra Monticciolo, chair of the American College of Radiology’s breast-imaging commission. Early studies had suggested CAD might improve detection by as much as 20 percent, but later research suggested no benefit and the possible harm.

“I don’t think radiologists will be that surprised. It’s been back-and-forth in the literature,” Monticciolo said.

Many radiologists dislike CAD screenings, which add tiny signs marking areas of concern to ordinary digital breast images, she said. But the tool often misses areas of true concern while flagging nonexistent problems, she added.

“They were trying to give us the latest technology,” Monticciolo said. “If you’re asking me in my own personal practice, most of us would not feel tremendously affected by not using CAD. We do not feel dependent on it.”

But Dr. Stephen Feig, director of breast imaging and a professor of radiology at the University of California at Irvine’s School of Medicine, said it was important not to discount the value of greater CAD detection of calcification and DCIS.

“DCIS are real cancers,” he said.

In the editorial accompanying the study, Dr. Joshua Fenton of the University of California at Davis’ Health System, who specializes in cancer-screening tests, said the study shows it’s time for the government to rethink spending public-health dollars on CAD.

“In a $3 trillion annual health-care system, CAD accounts for about $1 of every $10,000 spent on health care,” he wrote, adding: “Congress should therefore rescind the Medicare benefit for CAD use.”

CMS officials didn’t respond to questions about the potential impact of the study.

But Dr. Marc Mora, Group Health’s chief medical director for health-plan specialty administration, said he’ll take the results of the study to the committee that governs payment for about 45,000 mammograms performed there each year.

“We are likely to stop reimbursing,” he said.

Elmore published a 2007 paper that questioned the effectiveness of CAD and raised concerns that the device would result in more false positive screening results that could lead to unnecessary treatment for women.

She said she hopes the new study may change practice. In the meantime, she cautioned that women shouldn’t skip mammograms because of the CAD controversy.

“If women do want to get breast-cancer screening, mammography is the best and only well-studied breast-cancer exam,” she said.