The Mammogram Controversy Continues
Annual mammograms for women aged 40-59 don’t reduce the death rate from breast cancer, according to a new study.
The study, published on bmj.com, also said that 22 percent of breast cancers detected via mammogram were over-diagnosed—meaning that the cancers that were found were ones that would not cause symptoms or death.
The findings are fueling an ongoing debate about the benefits of mammograms.
Regular mammography screening is done to diagnose breast cancer and to reduce the number of deaths from the illness. Women with small (non-palpable) breast cancer detected by screening have better long term survival rates than women with palpable breast cancer. But it is not clear whether this survival difference is a consequence of organized screening or of lead time bias (when testing increases perceived survival time without affecting the course of the disease) and over-diagnosis.
The researchers, based in Toronto, Canada, analyzed breast cancer incidence and death in more than 89,000 women aged 40-59 who did or didn’t undergo mammograms.
Women in one group had a total of five mammography screens (one a year over a five-year period), while those in the control were not screened. Women aged 40-49 in the mammography group also got annual physical breast examination, while women of that same age in the control group, got a single examination.
During the 25 year study period, 3,250 women in the mammography arm and 3,133 in the control arm were diagnosed with breast cancer, and 500 and 505, respectively, died of breast cancer. "Thus, the cumulative mortality from breast cancer was similar between women in the mammography arm and in the control arm," the authors said.
At the end of the five year screening period, the researchers said, an “excess” of 142 breast cancers occurred in the mammography arm compared with the control arm, and at 15 years the excess remained at 106 cancers. This, say the authors, implies that 22% of the screen detected invasive cancers in the mammography arm were over-diagnosed.
The authors said their study indicated “that the rationale for screening by mammography should be urgently reassessed by policy makers."
The medical profession isn’t of one mind on the issue. The American Cancer Society recommends yearly mammograms starting at age 40, as well as physical breast exams every three years starting at age 20 and annually after age 40. The ACS also urges regular breast self-examinations.
The U.S. Preventive Services Task Force has recommended mammograms every two years for women aged 50 to 75. They also suggest that women under 50 talk with their health-care practitioner about the advisability of a mammogram.