Breast cancer screening tied to overdiagnosis
A new report suggests that when a breast cancer screening program was rolled out in Norway, up to 10 women were diagnosed and treated for cancer unnecessarily for every breast cancer death that was prevented.
That’s because when doctors screen for cancer in women who don’t have symptoms, it’s impossible for them to tell whether a tumor picked up by mammography will grow quickly into advanced cancer or will only progress slowly or not at all, said lead author Dr. Mette Kalager.
And although women are well-versed in the benefits of mammography, they aren’t always warned about the possible harms of so-called overdiagnosis and overtreatment, according to Kalager, a breast cancer surgeon and a visiting scientist at the Harvard School of Public Health in Boston.
“You have to really consider the benefit and the harm against each other, and really think through: what is my risk of dying from breast cancer, and what is my risk of being overdiagnosed?” she said.
The problem with treating tumors that would never cause any symptoms or cut women’s lives short is that women only experience harms with no health benefit, Kalager added.
“These women undergo treatment, that is surgery, radiotherapy, chemotherapy or hormone treatment for breast cancer, that they don’t really need,” she told Reuters Health.
“It’s not only the distress of being a cancer patient, but really the harms of treatment.”
LONDON - One in three breast cancer patients identified in public screening programs may be treated unnecessarily, a new study says. Karsten Jorgensen and Peter Gotzsche of the Nordic Cochrane Centre in Copenhagen analyzed breast cancer trends at least seven years before and after government-run screening programs for breast cancer started in parts of Australia, Britain, Canada, Norway and Sweden.
The research was published Friday in the BMJ, formerly known as the British Medical Journal. Jorgensen and Gotzsche did not cite any funding for their study.
Once screening programs began, more cases of breast cancer were inevitably picked up, the study showed. If a screening program is working, there should also be a drop in the number of advanced cancer cases detected in older women, since their cancers should theoretically have been caught earlier when they were screened.
However, Jorgensen and Gotzsche found the national breast cancer screening systems, which usually test women aged between 50 and 69, simply reported thousands more cases than previously identified.
Overall, Jorgensen and Gotzsche found that one third of the women identified as having breast cancer didn’t actually need to be treated.
Radiation therapy itself is linked to a slightly increased risk of cancer and chemotherapy comes with a range of side effects, from nausea and fatigue to a higher risk of infections.
“For years I think we’ve exaggerated the benefits (of mammography) and we’ve sort of downplayed or minimized the harms,” said Dr. H. Gilbert Welch, who studies cancer screening at the Dartmouth Institute for Health Policy & Clinical Practice in Lebanon, New Hampshire.
“The issue is no longer whether overdiagnosis occurs, it’s how often,” said Welch, the author of Overdiagnosed: Making People Sick in the Pursuit of Health, who wasn’t part of the new study team.
For the research, Kalager and her colleagues compared breast cancer diagnoses in counties in Norway that had or hadn’t started widespread screening between 1996 and 2005 - as well as in the ten years prior when none of the counties had a screening program in place, for comparison.
Another problem with the study was pointed out in the rapid responses on BMJ by Dr. Daniel B. Kopans, Professor of Radiology at the Harvard Medical School and the Massachusetts General Hospital. I noticed this problem, too, but couldn’t formulate it as clearly at first. The problem is that this study is not looking at a fixed cohort of women before and after screening began. Consequently, every year, new women turn 50 and begin screening, and screened women “age out” of the screening system. Finally, another huge confounder that I don’t think that Jørgensen and Gøtzsche adequately account for is the use of hormone replacement therapy and the decrease in inherent breast cancer incidence that has begun since the report from the Women’s Health Initiative study that found increased risk of breast cancer, heart disease, stroke and blood clots in women taking hormone replacement therapy (HRT) led to a dramatic decrease in the number of women using HRT.
Don’t get me wrong. There is no doubt that mammographic screening programs produce a rate of overdiagnosis. The question is: What is the rate? Unfortunately, the most accurate way to measure the true rate of overdiagnosis would be a prospective randomized trial, in which one group of women is screened and another is not, that follows both groups for many years, preferably their entire life. Such a study is highly unlikely ever to be done for obvious reasons, namely cost and the fact that there is sufficient evidence to show that mammographic screening reduces breast cancer-specific mortality for women between the ages of 50 and 70 at least, the latter of which would make such a study unethical. Consequently, we’re stuck with retrospective observational studies, such as the ones analyzed in this systematic review. One trial that has a stronger design, as far as I’m concerned, was reported in 2006 by Zackrisson et al entitled Rate of over-diagnosis of breast cancer 15 years after end of Malmö mammographic screening trial: follow-up study, which found a rate of overdiagnosis of between 10% and 18%, depending upon how the data were analyzed. For one thing, the Malmö study has the advantage of looking at individual women over time randomized to screening or no screening, rather than population-level numbers, as well as having a 15 year followup. Its disadvantage is that the Malmö mammographic screening trial was one of the classic ongoing studies, for which the screening occurred between the years 1976 to 1986. In the interim, mammography has become more sensitive, with improved imaging and digital mammography. Consequently, it is quite possible that the rate of overdiagnosis is higher than what was reported in the followup to the Malmö study.
Starting in four out of 19 counties, mammography was offered to all women between the ages of 50 and 69.
In the United States, the government-backed U.S. Preventive Services Task Force recommends screening women age 50 to 74 every other year, although some other organizations still call for regular mammograms for all women starting at 40.
In counties that didn’t start offering screening until after the study period, there was an 18 percent increase in the number of breast cancers diagnosed between 1986 to 1995 and 1996 to 2005 - possibly because of increased use of menopause drugs that have been tied to cancer, the researchers explained.
In comparison, 47 percent more breast cancers were diagnosed in counties that rolled out screening programs during that time period, Kalager’s team reported Monday in the Annals of Internal Medicine.