TUESDAY, Sept. 13 (HealthDay News) -- One of the goals of mammograms is detecting breast cancer early enough to avoid needing a mastectomy. But a new Norwegian study suggests that mastectomy rates climb higher as more women undergo the screening test.

Using national cancer data for more than 35,000 women aged 40 to 79 who were diagnosed with early or invasive breast cancers, Oslo researchers found a 31 percent increased risk of mastectomy in women invited to screening compared with a non-invited younger age group. The Norwegian breast cancer screening program began in 1996 in four counties, encompassing the country's remaining 15 counties by 2004.

While scientists did not investigate why mastectomy rates climbed in screened groups, study author Pal Suhrke said the main reason is likely "cancer overdiagnosis," or the detection and subsequent treatment of tumors that might grow very slowly and not pose much of a risk.

"Since the introduction of screening is associated with a more than 50 percent increase in breast cancer rates, some of these women are treated by mastectomy," said Suhrke, a doctoral candidate in the pathology department at Oslo University Hospital. "For many, these results are surprising and disappointing because one might suspect that due to earlier detection of tumors, the number of women needing mastectomies would decrease."

The study is published in the Sept. 13 online edition of BMJ.

Suhrke and his colleagues found that the country's annual mastectomy rate rose by 9 percent in women aged 50 to 69 -- the group invited to screening -- between the pre-screening period from 1993 to 1995 and the introduction of biennial screening from 1996 to 2004.

In contrast, mastectomy rates fell by 17 percent in non-invited women aged 40 to 49 and 13 percent in non-invited women aged 70 to 79.

Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, said the study raises some valid points, but "they haven't addressed all the issues," such as the idea that some breast cancer patients opt for more radical surgery because they don't want to worry about the potential for recurrence of even early-stage cancers.

The researchers also noted that some Norwegian women in the study didn't live near a radiation center, Bernik said, making mastectomy a safer option because follow-up radiation treatments were not otherwise accessible. Breast reconstruction techniques have also improved greatly in the past decade, she added.

"I think it's true, if you screen more you're going to find more cancers. That ultimately should lead to better survival for these patients," she said. "Mastectomy is not as dreadful a choice as it used to be."

Indeed, a recent study by the Mayo Clinic indicated that few breast cancer survivors who opt for a double mastectomy as a precautionary measure regretted their decision decades later. Twenty years after surgery, 92 percent said they would make the same decision, according to preliminary findings presented at the American Society of Breast Surgeons' annual meeting in April.

Bernik cautioned that the take-home message of the Norwegian study isn't that women shouldn't get screened. While mammograms do find some early-stage cancers that may never progress, and those women go on to be treated anyway -- "you can't pick and choose which ones are going to be a problem or not . . . and so there is going to be an element of overtreatment," she said.

"I think we should continue screening and work toward ways of potentially trying to figure out who needs more extensive surgery," Bernik added.

More information

Learn more about breast reconstruction surgery after mastectomy from the American Cancer Society.