The number of early breast tumors detected by mammogram hasn’t led to a corresponding reduction of advanced cancer, findings that suggest increased screening has led to over diagnosis and unneeded treatment, researchers said.
Mammograms have doubled the number of early-stage breast cancers detected in the U.S. each year, while the rate of advanced disease has declined just 8 percent annually, according to a study published yesterday in the New England Journal of Medicine. One third of breast cancers detected and treated posed no threat to health, the research also found.
The study backs the 2009 guidelines by the U.S. Preventive Services Task Force that advise against routine mammograms for women ages 40 to 49 who aren’t at increased risk for breast cancer. The task force made the recommendations because of high rates of false-positive results leading to unnecessary biopsies and anxiety. Some medical and advocacy groups have opposed the guidelines on the grounds that more screening saves lives.
“We believe we’ve supported the more conservative guidelines reducing the mammograms in a woman’s lifetime from about 40 to about 13 and thereby not only reducing the other risks but the risk of over diagnosis,” said Archie Bleyer, the lead author of the study and chairman of the Institutional Review Board at St. Charles Health System in Bend, Oregon. Bleyer also is a clinical research professor in the Department of Radiation Medicine at Oregon Health and Science University in Portland.
The task force, an independent medical advisory group to the government, suggests women have a mammogram once every two years from ages 50 to 74, while the American Cancer Society suggests yearly mammograms starting at age 40.
The findings drew criticism from the American College of Radiology, who called the study methods “flawed.” Just looking at the trends of advanced cancer in proportion to other stages of cancers isn’t enough to predict whether mammograms are saving lives, said Barbara Monsees, chairwoman of the American College of Radiology Breast Imaging Commission and a professor of radiology at Washington University in St. Louis.
“At this point in time we really don’t have a choice anyway,” Monsees said in a telephone interview. “It’s not the fault of screening that we’re finding cancers that may not advance and kill people. Right now we don’t know how to differentiate those cancers from other cancers, the killing cancers, basically we’re treating them all the same. I don’t think it should stand in the way of women getting screened.”
Women diagnosed with breast cancer undergo surgery, radiation therapy, hormonal therapy for five years or more, chemotherapy or a combination of these treatments whether the cancer is harmful or not, Bleyer said.
“It is a lot easier to make a simple and misleading case for screening, than it is to try to do better,” Bleyer said. “But it is not in the best interest of our patients.”
The researchers in the study used U.S. federal data to look at the incidence of early-stage and advanced breast cancer from 1976 to 2008 in women 40 years and older.
They found that the introduction of mammogram in the U.S. doubled the number of cases of early-stage breast cancer detected each year to 234 cases per 100,000 women from 112 cases, an increase of 122 cases per 100,000 women. The rate of advanced cancer fell to 94 cases per 100,000 women a year from 102 cases. That increase in early breast cancers diagnosed didn’t lead to a corresponding drop in advanced cases, the researchers said. Only eight of 122 additional early-stage cancers would progress to advanced disease.
The researchers estimated that breast cancer has been over diagnosed in 1.3 million women in the U.S. in the past 30 years. In 2008, more than 70,000 were over diagnosed with the disease, accounting for about 31 percent of all breast cancers diagnosed, according to the study.
Monsees said over diagnosis is probably between 10 percent and 15 percent and pointed out that women shouldn’t be disheartened by this kind of study.
The study also showed that fewer women are dying from breast cancer but that finding may be because of better breast cancer treatments than screening.
“Screening is definitely beneficial, it does save lives but we’re overdoing it and as a result, have a greater problem of over diagnosis,” Bleyer said.