The paper (Bleyer and Welch, 2012).
Abstract:
Background
To reduce mortality, screening must detect life-threatening disease at an earlier, more curable stage. Effective cancer-screening programs therefore both increase the incidence of cancer detected at an early stage and decrease the incidence of cancer presenting at a late stage.
Methods
We used Surveillance, Epidemiology, and End Results data to examine trends from 1976 through 2008 in the incidence of 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.
Results
The introduction of screening mammography in the United States has been associated with a doubling in the number of cases of early-stage breast cancer that are detected each year, from 112 to 234 cases per 100,000 women — an absolute increase of 122 cases per 100,000 women. Concomitantly, the rate at which women present with late-stage cancer has decreased by 8%, from 102 to 94 cases per 100,000 women — an absolute decrease of 8 cases per 100,000 women. With the assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were 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, we 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 U.S. women in the past 30 years. We estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31% of all breast cancers diagnosed.
Conclusions
Despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer. Although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers, and that screening is having, at best, only a small effect on the rate of death from breast cancer.
There is a related case study on mammography screening in the same issue of the journal.
With all the Bayesian experts here, it should be a no-brainer to figure out what to make of the recent study (popular description). It says that, despite doubling early detection rates, late stage cancers declined by barely 8%, so most new early detections are effectively false positives, i.e. they would not develop into a life-threatening condition if left untreated.
Some contradictory quotes:
"We've suggested to women that having a mammogram is one of the most important things you can do for your health, and that's simply not true," Welch says. "I can't tell you the right thing to do, except to tell women the truth, tell them both sides of the story. We shouldn't be scaring women. This is a really close call."
Eric Winer, head of breast medical oncology at Boston's Dana-Farber Cancer Institute, notes that the study found an 8% reduction in the number of women whose tumors were detected at more advanced stages. Even under a scenario in which mammograms led more than 1 million women to receive unnecessary treatment, the screenings would have prevented 410,000 diagnoses of late-stage cancer.
Though women have been instructed that "early detection saves lives," relatively few are told that screenings also have costs, including the risk of undergoing surgery, radiation and drug therapy that doesn't help them, Kramer says. "The risks of overdiagnosis are real, and women ought to know about it," Kramer says.
Given the test's limitations, Winer says, women may choose to have fewer screenings to reduce their risk. "It certainly suggests that a woman who chooses to wait until she's 50 to have mammograms, or who chooses to have mammograms every other year, is making a rational decision," Winer says.
“We’re coming to learn that some cancers — many cancers, depending on the organ — weren’t destined to cause death,” said Dr. Barnett Kramer, a National Cancer Institute screening expert. However, “once a woman is diagnosed, it’s hard to say treatment is not necessary.”
“We are left to conclude, as others have, that the good news in breast cancer — decreasing mortality — must largely be the result of improved treatment, not screening,”
“Instead, we’re diagnosing a lot of something else — not cancer” in that early stage, Bleyer said. “And the worst cancer is still going on, just like it always was.”
Another expert, Dr. Linda Vahdat, director of the breast cancer research program at Weill Cornell Medical College in New York, 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,” she said.