Breast Cancer May Not Be as Overdiagnosed as Previously Thought

New research finds overdiagnosis occurs in 15 percent of cases detected using mammograms

A nurse administering a mammogram
Over the past decade, scientists have debated how often overdiagnosis occurs in screenings, with the most widely cited estimates at about 30 percent. New research suggests overdiagnosis occurs in 15 percent of breast cancer screenings. Getty Images / andresr

Patients that have routine mammograms can catch breast cancer in its early stages, reducing their risk of dying from the disease. But mammography screenings can also cause doctors to prescribe unnecessary tests and treatments for tumors that would not have progressed or for tumors that would have progressed, but not caused symptoms in a patient's lifetime. 

Over the past decade, scientists have debated how often this overdiagnosis occurs in screenings, with the most widely cited estimates at about 30 percent, per a statement. 

“The range was from zero to 54 percent, so a huge range and virtually no consensus as to what the true rate [of overdiagnosis] was,” Marc Ryser, a population health scientist at Duke University, tells STAT News’ Angus Chen. 

A new study published in Annals of Internal Medicine shows this happens far less than previously thought—about 15 percent of screen-detected breast cancers are overdiagnosed in the United States. 

Scientists from Duke University and the Fred Hutchinson Cancer Research Center analyzed data from 35,986 women 50 to 74 years old. This included 82,677 mammograms and 718 breast cancer diagnoses. The researchers built a model that estimated the tumors that don’t progress, the number that do and the time it takes for symptoms to pop up, per STAT News. They found that among women who were screened every two years, approximately 1 in 7 screen-detected cases is overdiagnosed. 

Of those breast cancers overdiagnosed, about a third were nonprogressive, or small tumors that wouldn’t have caused problems, senior author Ruth Etzioni, a biostatistician at the Fred Hutchinson Cancer Research Center, says in a video. The rest were progressive, but wouldn’t have led to symptoms within the patient’s lifetime. 

“Honestly, [the study] is reassuring,” Michael Hassett, an oncologist at the Dana-Farber Cancer Institute who did not work on the study, tells STAT News. “Most of the cases we’re finding are not overdiagnosis cases and most are true cases. The problem we’re left with is less about overdiagnosis and more about how do we tailor the intensity of treatment to intensity of cancer.”

Overdiagnosis still represents a real risk, Ryser, who is an author on the study, says in a video, but doctors and patients should make informed decisions that weigh both the benefits and the risks of screenings. 

“The most widely covered estimate of breast cancer overdiagnosis in the U.S. was inflated, and this is unfortunate because it led to a great deal of confusion among women about the value of screening mammography,” Etzioni says in the video “We hope our study clears this up.”