Overdiagnosis of Breast Cancer Is Rife

A new study claims that as a result of mammographic screening programs over the past 30 years, overdiagnosis plays a part in up to a third of all newly discovered tumors.

Researchers at Oregon Health and Science University (OHSU; Portland, USA) and Dartmouth University (Hanover, NH, USA) used the Surveillance, Epidemiology, and End Results (SEER) data to examine incidence trends in breast cancer diagnosis from 1976 through 2008, as related to early-stage breast cancer (ductal carcinoma in situ and localized disease) and late-stage breast cancer (regional and distant disease), among women 40 years of age or older.

The results showed that the introduction of screening mammography in the United States was associated with a doubling in the number of cases of early-stage breast cancer detected each year, from 112 to 234 cases per 100,000 women. At the same time, the rate at which women present with late-stage cancer has decreased by 8%, from 102 to 94 cases per 100,000 women. Based on the assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were actually expected to progress to advanced disease.

After excluding the transient excess incidence associated with hormone-replacement therapy and adjusting for trends in the incidence of breast cancer among women younger than 40 years of age, the researchers estimated that breast cancer was overdiagnosed, i.e., tumors were detected on screening that would never have led to clinical symptoms--in 1.3 million US women in the past 30 years. On a yearly basis, the researchers estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women, accounting for 31% of all breast cancers diagnosed. The study was published in the November 22, 2102, issue of the New England Journal of Medicine (NEJM).

“Breast cancer mortality has been falling in the US, a decline usually attributed to a combination of increased screening and better treatment; the study implies that treatment ... is the main, if not the only, reason for the improvement,” said lead author Archie Bleyer, MD, of OHSU. “The assumptions in the study are conservative and doctors and patients need to be aware of the harm associated with overdiagnosis, as well as any potential benefit from early diagnosis.”

According to the authors, the remedy for the overdiagnosis of breast cancer would be to reduce the scope of mammographic screening in line with the 2009 recommendations of the US Preventive Services Task Force (USPSTF; Rockville, MD, USA), which recommended against routine screening mammography for women younger than 50, and recommended screening interval for women 50 and older should be every two years instead of annually.

Related Links:
Oregon Health and Science University
Dartmouth University
US Preventive Services Task Force