A 65-year-old patient gets a mammogram

A 65-year-old patient gets a mammogram (Heather Charles, Chicago Tribune / April 2, 2012)

NEW YORK (Reuters Health) - A new report suggests that when a breast cancer screening program was rolled out in Norway, up to 10 women were diagnosed and treated for cancer unnecessarily for every breast cancer death that was prevented.

That's because when doctors screen for cancer in women who don't have symptoms, it's impossible for them to tell whether a tumor picked up by mammography will grow quickly into advanced cancer or will only progress slowly or not at all, said lead author Dr. Mette Kalager.

And although women are well-versed in the benefits of mammography, they aren't always warned about the possible harms of so-called overdiagnosis and overtreatment, according to Kalager, a breast cancer surgeon and a visiting scientist at the Harvard School of Public Health in Boston.

"You have to really consider the benefit and the harm against each other, and really think through: what is my risk of dying from breast cancer, and what is my risk of being overdiagnosed?" she said.

The problem with treating tumors that would never cause any symptoms or cut women's lives short is that women only experience harms with no health benefit, Kalager added.

"These women undergo treatment, that is surgery, radiotherapy, chemotherapy or hormone treatment for breast cancer, that they don't really need," she told Reuters Health.

"It's not only the distress of being a cancer patient, but really the harms of treatment."

Radiation therapy itself is linked to a slightly increased risk of cancer and chemotherapy comes with a range of side effects, from nausea and fatigue to a higher risk of infections.

"For years I think we've exaggerated the benefits (of mammography) and we've sort of downplayed or minimized the harms," said Dr. H. Gilbert Welch, who studies cancer screening at the Dartmouth Institute for Health Policy & Clinical Practice in Lebanon, New Hampshire.

"The issue is no longer whether overdiagnosis occurs, it's how often," said Welch, the author of Overdiagnosed: Making People Sick in the Pursuit of Health, who wasn't part of the new study team.

For the research, Kalager and her colleagues compared breast cancer diagnoses in counties in Norway that had or hadn't started widespread screening between 1996 and 2005 — as well as in the ten years prior when none of the counties had a screening program in place, for comparison.

Starting in four out of 19 counties, mammography was offered to all women between the ages of 50 and 69.

In the United States, the government-backed U.S. Preventive Services Task Force recommends screening women age 50 to 74 every other year, although some other organizations still call for regular mammograms for all women starting at 40.

In counties that didn't start offering screening until after the study period, there was an 18 percent increase in the number of breast cancers diagnosed between 1986 to 1995 and 1996 to 2005 — possibly because of increased use of menopause drugs that have been tied to cancer, the researchers explained.

In comparison, 47 percent more breast cancers were diagnosed in counties that rolled out screening programs during that time period, Kalager's team reported Monday in the Annals of Internal Medicine.

WOMEN â┬Ç┬śMISINFORMED'

When they followed women to see whether the number of cancers in the no-screening group caught up with the number spotted during mammograms, the researchers found that it didn't.

From the difference in cancer rates between women who were screened and those who weren't, they concluded that 15 to 25 percent of the cancers caught by screening wouldn't have become symptomatic or life-threatening.

They calculated that for every 2,500 women invited to get screened over ten years, there would be 20 cases of life-threatening breast cancer caught and one breast cancer death prevented. Among that same group of women, between six and 10 would be diagnosed and treated for a tumor that never would have caused them any problems.