TUESDAY, Feb. 12 (HealthDay News) -- Many women diagnosed with a precancerous breast lesion known as ductal carcinoma in situ (DCIS) are highly anxious about their prognosis, even though they face a low risk of a recurrence or of developing invasive breast cancer, a new study finds.

"Many of these women are living as if they're waiting for the other shoe to drop," said lead researcher Dr. Ann Partridge, an oncologist at the Dana-Farber Cancer Institute and Brigham & Women's Hospital, in Boston.

Her team published the findings Feb. 12 in the online edition of the Journal of the National Cancer Institute.

The study noted that 28 percent of the participants "believed that they had a moderate or greater chance of DCIS spreading to other places in their bodies, despite the fact that metastatic breast cancer actually occurs following a diagnosis of DCIS less than 1 percent of the time."

DCIS involves abnormal cells in the lining of the breast duct that have not spread outside the duct, according to the National Cancer Institute. In 2006, DCIS accounted for more than 20 percent of all diagnoses linked to breast cancer in the United States -- about 62,000 cases, the study reported.

The increasing percentage of DCIS diagnoses over the last 20 years or more has been attributed to improved detection from the increasing use of screening mammography, experts say.

But all too often, women are unnecessarily frightened by a DCIS diagnosis, said the authors of the study, which involved almost 500 women newly diagnosed with DCIS.

"In the complex treatment decision-making process, it is often possible to lose sight of the fact that DCIS poses limited risks to a woman's overall mortality," the study authors noted.

Nevertheless, approximately 38 percent of those surveyed thought they had at least a moderate risk of getting an invasive cancer over the next five years, and 53 percent reported intrusive or avoidant thoughts about DCIS. That number declined to 31 percent 18 months after diagnosis, the researchers said.

Among the 487 study participants who were newly diagnosed with DCIS, 34 percent had undergone a mastectomy, 50 percent had radiation therapy, and 43 percent reported taking tamoxifen to reduce their chances of breast cancer. The type of treatment or combination varied by surgeon, hospital volume and geographic region, the study explained.

"Although decision-making about treatment is complex, there is little doubt that women will be limited in their ability to participate in informed decision-making if they harbor gross misperceptions about the health risks they face," the study authors said. Researchers found a "strong relationship between distress and inaccurate risk perceptions," they added.

One of the difficulties of such measures of anxiety about DCIS is that the study did not determine what these patients had learned from their physicians or from other sources -- such as the Internet -- about DCIS, and how accurate that information was, said Michael Stefanek, vice president of behavioral research for the American Cancer Society.

The choice of treatment depends upon the characteristics of the patient and the lesion, added Partridge, who is also an assistant professor of medicine at Harvard Medical School. The dilemma posed by the prospect of under- or over-treating DCIS is complicated by medicine's current inability to distinguish between "good actors and bad actors" -- lesions that don't recur or go on to become invasive breast cancer and those that do, she added.

Another expert agreed with that assessment.

Everyone would be more comfortable if there wasn't such a "big gray zone" between what is normal tissue and what is invasive cancer, said Dr. H. Gilbert Welch, a professor of medicine at Dartmouth Medical School and an expert on how well health care works for patients. Welch argued that as mammography continues to detect smaller and smaller DCIS lesions, there can be a tendency to over-treat. He recommends that the diagnostic threshold for DCIS be raised to doing biopsies on only lesions that measure 1 centimeter or greater in diameter.

"There is this ironic finding that women with this early precursor lesion may be treated more aggressively than women with invasive breast cancer," he said. "They may have mastectomies instead of just a lumpectomy. At some level we have to say, 'Does this really make sense?'"

Another study in the same issue of JNCI suggests that medical science is winning the war on breast cancer. The research, which involved nearly 5,000 breast cancer patients, was led by the National Cancer Institute of Canada's Clinical Trials Group. A total of 256 of the participants died during the four-year study.

The researchers found that older women who had survived for at least five years after a diagnosis of early stage breast cancer were most likely to die of causes unrelated to their breast malignancy. In fact, 60 percent of these deaths were not caused by breast cancer, the Canadian team found.

More information

For more on DCIS, head to the U.S. National Cancer Institute.