Routine mammograms may result in significant overdiagnosis of invasive breast cancer

New Harvard School of Public Health (HSPH) research suggests that routine mammography screening—long viewed as an essential tool in detecting early breast cancers—may in fact lead to a significant amount of overdiagnosis of disease that would otherwise have proved harmless. Based on a study of women in Norway, the researchers estimate that between 15% and 25% of breast cancer cases are overdiagnosed.

The study appears in the April 3, 2012 issue of the Annals of Internal Medicine.

"Mammography might not be appropriate for use in screening because it cannot distinguish between progressive and non-progressive cancer," said lead author Mette Kalager, a visiting scientist at HSPH and a researcher at the Telemark Hospital in Norway. "Radiologists have been trained to find even the smallest of tumors in a bid to detect as many cancers as possible to be able to cure breast cancer. However, the present study adds to the increasing body of evidence that this practice has caused a problem for women—diagnosis of breast cancer that wouldn't cause symptoms or death."

Most women in the U.S. begin having annual mammograms in their 40s or 50s. But recent research suggesting evidence of overdiagnosis has increased debate about the benefits of screening. A number of experts have speculated that new effective treatments for breast cancer play a larger role in saving women's lives than screening does—and have noted that overdiagnosis can cause unnecessary stress and unnecessary medical treatment.

Kalager says the new findings suggest that women should be well-informed not only about the potential benefit from mammography, but also about its possible harms—including mental distress, biopsies, surgeries, or chemotherapy and hormone treatments for disease that would never have caused symptoms.

The researchers analyzed data from 39,888 women with invasive breast cancer in Norway, 7,793 of whom were diagnosed during the 10-year rollout of the Norwegian Breast Cancer Screening Program, which began in 1996, for women ages 50 through 69. Because the screening program was phased in over time, the researchers were able to compare the number of breast cancer cases in women who had been offered screening with those not offered screening. The remaining study population consisted of two historical-comparison groups—mirroring the current groups—of women diagnosed with breast cancer from 1986 through 1995, before the nationwide program began.

The researchers theorized that if mammography is beneficial, it would lead to a decrease in late-stage breast cancer cases—the theory being that early detection prevents late-stage disease.

But the researchers did not find a reduction in late-stage disease in women who'd been offered screening. They did find, though, a substantial amount of overdiagnosis; among the 7,793 women diagnosed with breast cancer through participation in the , 15% to 25% were overdiagnosed—between 1,169 and 1,948 women. Based on those numbers, they further estimated that, for every 2,500 women invited to screening, 2,470 to 2,474 will never be diagnosed with breast cancer and 2,499 will never die from breast cancer. Only one death from breast cancer will be prevented. But 6 to 10 will be overdiagnosed, and treated with surgery, radiation therapy, and possibly chemotherapy without any benefit.

Other HSPH authors included senior author Rulla Tamimi, assistant professor in the Department of Epidemiology, and Hans Olov-Adami, professor of epidemiology.

Support for the study was provided by the Norwegian Research Council and Frontier Science.

More information: "Overdiagnosis of Invasive Breast Cancer Due to Mammography Screening: Results From the Norwegian Screening Program," Mette Kalager, Hans-Olov Adami, Michael Bretthauer, Rulla Tamimi, Annals of Internal Medicine, online April 2, 2012.

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A2G
not rated yet Apr 03, 2012
Combine this study with the fact that five year survival rates for chemo treatment are so poor means that a lot of women who would of otherwise lived to a good old age without any symptoms are now dead?

When is there going to be any real progress in treating cancer?

My own mother had both of her breasts taken years ago over a pea sized lump. The butchers did this do her even though there was no evidence ever found that it had spread any where beyond the lump remove. Hell it might even of not been cancer?

Thankfully they didn't give her chemo or radiation or I believe that I would not have my mom with me today.

BTW: The $urgery was in 1975 when she was in her forties. My mom is now 89. All they had to do was remove the pea sized lump. Not the hack job they did. The original butcher wanted to remove her ovaries as well without any proof they were affected. A$$hole.

Got it all stopped with the help of another doctor who stopped it.

It was all so unnecessary and clearly driven by $