In a study recently published in the New England Journal of Medicine, researchers at the Dartmouth Medical School and the Oregon Health & Science University found that screening mammography, “has only marginally reduced the rate at which women present with advanced cancer,” the authors write. The study results suggest that up to one-third of breast cancer cases, or 50,000 to 70,000 cases per year, do not need treatment.
The researchers state that mammography screening has doubled the number of cases of early-stage breast cancer detected each year, from 112 to 234 cases per 100,000 women. However, the researchers report that late-stage cancer has dropped just 8%.
Per the researchers, this imbalance suggests that breast cancer was overdiagnosed (meaning, tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million women in the United States over the past 30 years; the authors estimate that in 2008, breast cancer was overdiagnosed in more than 70,000 women, or 31% of all breast cancers diagnosed. If screening were working, there should be one fewer patient diagnosed with late-stage cancer for every additional patient whose cancer was found at an earlier stage.
However, in an Associated Press article on the findings, the Dr. Linda Vahdat, the Director of the Breast Center Research Program and Chief of the Solid Tumor Service at Weill Cornell Medical College, said the study’s leaders made many assumptions to reach a conclusion about overdiagnosis that “may or may not be correct.”
“I don’t think it will change how we view screening mammography,” Dr. Vahdat said.