According to a new study from Norway up to a fourth of breast cancers found through mammograms are harmless and would not cause noticeable disease during the women's lifetimes. Such women are said to be over-diagnosed, because their cancers would not have caused symptoms or death. Over-diagnosis is a problem because women may receive tests and treatment they did not actually need.
That said, researchers agree that they have no way of knowing which women have these cases; the study showed that it's statistically probable that such cases are occurring. “These women are treated with all the harms of treatment, and without the benefit of it,” said study researcher Mette Kalager, at the Telemark Hospital in Norway.
In the study, for every 2,500 women who underwent mammogram screening over a 10-year period, 20 cases of breast cancer were identified that would have caused significant disease if they went undetected, and one death was prevented. However, 6 to 10 cases of over-diagnosis occurred. “You have to weigh the benefits and the harms, and you have to make up your mind [about] what is most important for you,” Kalager said.
At present the U.S. Preventive Services Task Force recommends women ages 50 to 74 receive a mammogram every two years, while the American Cancer Society recommends yearly mammograms beginning at age 40. “When you look for cancer early and you look really hard, you find forms that are ultimately never going to bother the patient,” said Dr. H. Gilbert Welch of the Dartmouth Institute for Health Policy and Clinical Practice, who was not part of the research. “It's a side effect of early diagnosis.” Previous studies have found that rates of over-diagnosis from mammograms vary, from 0 percent to 54 percent, Kalager said.
In the new study, Kalager and colleagues analyzed cases of invasive breast cancer that occurred in Norway between 1996 and 2005, a time period over which the country began a breast cancer screening program for women ages 50 to 69. Different regions of the country began the screening program at different times, and the researchers compared cases among women who had been offered screening with those not offered screening.
About 7,800 women were diagnosed with breast cancer during the 10-year study period. Of these, the researchers estimated between15 percent and 25 percent were over-diagnosed — in other words, between 1,169 and 1,948 women would never have faced illness due to their cancers.
But while a doctor might consider the diagnosis of a cancer that never causes symptoms or death to be over-diagnosis, from a patient's perspective, it might be exactly what they want “because they want control of their lives,” said Dr. Leo Twiggs, a professor of obstetrics and gynecology at the University of Miami School of Medicine, who was not involved in the study. A person who is diagnosed with pre-cancer might want to change their behavior, such as increasing the frequency of their mammograms, Twiggs said.
Because screening is started earlier in the United States than in Norway, over-diagnosis probably occurs more often here, according to Dr. Joann Elmore, of the University of Washington School of Medicine in Seattle, and Dr. Suzanne Fletcher, of Harvard Medical School in Boston, who wrote an editorial accompanying the study.
A “watch and wait” approach may also be tough for anxious patients, or for radiologists who don't want to be sued if they miss signs of disease, Elmore and Fletcher said in the editorial. “Nevertheless, unless serious efforts are made to reduce the frequency of over-diagnosis, the problem will probably increase,” as new imaging techniques are introduced, they wrote. “We have an ethical responsibility to alert women to this phenomenon,” they wrote. The study and editorial are published in the April 3 issue of the Annals of Internal Medicine.
The national cancer director for England, Prof Mike Richards, has announced a review into breast cancer screening. Dr Julie Sharp, Cancer Research UK's senior science information manager, said, “Cancer Research UK is working with the National Cancer Director on an independent review of breast screening. Women need more accurate, evidence-based and clear information to be able to make an informed choice about breast screening. The decision whether to be screened is a personal one and that decision should be made with all of the potential harms and benefits fully explained. Until we have the results of the review, Cancer Research UK's position is that we remain supportive of breast screening.”
Dr Caitlin Palframan, policy manager at Breakthrough Breast Cancer, said, “The rate of overdiagnosis in breast cancer screening has been debated widely and led to confusing messages for women on the effectiveness of breast screening. However, we believe that screening is vital as it helps detect breast cancer early when treatment options are likely to be less aggressive and have more successful outcomes.”
Increased emotional sensitivity linked to previous COVID-19 infection, new research suggests