Routine mammography screening leads to a “substantial amount of overdiagnosis” of non-life threatening breast cancer, according to new research from the Harvard School of Public Health.
The Harvard study found that between 15% and 25% of breast cancer cases were overdiagnosed as a result of mammography screening. Specifically, up to 10 women were diagnosed and treated for cancer unnecessarily for every breast cancer death that was prevented.
“These women undergo treatment, that is surgery, radiotherapy, chemotherapy or hormone treatment for breast cancer, that they don’t really need,” said lead author Mette Kalager, who is a researcher at Telemark Hospital in Norway and a visiting scientist at Harvard.
“Mammography might not be appropriate for use in breast cancer screening because it cannot distinguish between progressive and non-progressive cancer,” explained Kalager. “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.”
As part of the study, Kalager and her research team examined data from nearly 40,000 women in Norway. Aged 50 to 69 years, the Norwegian women participated in a nationwide mammography screening program from 1996 to 2005.
Researchers estimate that for every 2,500 women who had a mammogram, 6 to 10 women were overdiagnosed, and treated with radiation, surgery or chemotherapy even though their cancers were not life threatening. The researchers also estimate that 20 women (out of 2,500) were correctly diagnosed with invasive breast cancer but were not overdiagnosed, and one death from breast cancer was prevented.
In an accompanying editorial, Joann Elmore, MD, of the University of Washington and Suzanne Fletcher, MD, of Harvard Medical School, wrote that radiologists need better tools to distinguish between cancers that need immediate treatment and those that can be safely observed over time. They should also consider changing the threshold at which a lesion is called abnormal and a biopsy performed. “We cannot wait for these tools to be developed,” they wrote. “It is time to agree that any amount of overdiagnosis is serious and to start dealing with this issue now.”
Current guidelines from the American Cancer Society recommend yearly mammograms starting at age 40.
The results of the Norwegian Breast Cancer Screening Study are being published in the Annals of Internal Medicine.