Damian Dovarganes / AP file
A large Canadian study questioning the value of annual screening mammograms made news across the world this week, leaving women confused about what to believe and do.
The new study, a 25-year follow-up of 90,000 women, found no difference in death rates between women who got annual screening mammograms and those who did not. “The data suggest the value of mammography screening should be reassessed,” wrote researchers.
Many breast cancer researchers and physicians agree that health professionals need to do a better job making sure women understand the risks and limitations of screening mammograms, which include finding some abnormalities that aren’t life-threatening and missing some that are.
But many also strongly believe in mammography’s benefits.
“Mammography is not perfect, but it’s the best tool we have, and we’re working on ways to make it better,” said Dr. Julie Gralow, director of breast medical oncology at the Seattle Cancer Care Alliance and a member of Fred Hutchinson Cancer Research Center’s Clinical Research Division. The Seattle Cancer Care Alliance supports the American Cancer Society’s recommendation that women begin annual mammography screening at age 40.
Combined data from previous clinical trials show that mammography reduces breast cancer deaths by 15 percent in women in their 40s and around 20 percent for older women.
But the new study, published Tuesday in BMJ by researchers from the University of Toronto, Women’s College Hospital in Toronto and The Hospital for Sick Children in Toronto, found that screening with yearly mammograms “does not result in a reduction in breast cancer specific mortality for women aged 40-59 beyond that of a physical examination alone or usual care in the community.”
An accompanying editorial by breast cancer researchers at the University of Oslo in Oslo, Norway, noted that this trial, which started in the 1980s, took place in the era of estrogen-blocking drugs and other treatment advances and said that in countries where such care is available mammography should be “urgently reassessed by policy makers.”
Not so fast, say other breast cancer researchers.
Dr. Ruth Etzioni, a biostatistician with Fred Hutch’s Public Health Sciences Division, described the new study as “a 25-year follow-up of an old study” and said that the media both overplayed its importance and downplayed its limitations.
The original clinical trial, called the Canadian National Breast Screening Study, was conducted in six Canadian provinces from 1980 to 1985. The trial enrolled 89,835 women, aged 40 to 59, randomly assigned to five annual mammography screens or to a control group that received no mammograms. (Women in both groups received regular physical breast examinations by trained nurses.)
After the five-year trial ended in 1985, the study group continued to collect data on cancer diagnoses and deaths through 2005. However, Etzioni pointed out that after 1985, women in both groups had the same access to mammography. So for most of the follow-up period, both groups were likely monitored the same way.
Etzioni’s takeaway: “Women should stick with their mammograms, and look at the study in the broader context of all the studies done on mammograms.”
The American Cancer Society and the U.S. Preventive Task Force have said that they will be reviewing all studies of mammograms and deciding whether to revise guidelines over the next year. (The federal task force set off an earlier round of confusion—and criticism—in 2009 when it recommended against routine mammograms for women in their 40s and biennial rather than yearly screenings for women aged 59 to 74.) Etzioni is a member of the ACS’s mammography guidelines panel.
Early detection remains important
Both Etzioni and Gralow had other problems with the new study’s assumptions, especially the belief that with advances in treatment, it’s less important to find breast cancers early.
“If you find cancer earlier, you have a better chance of needing a lumpectomy, not a mastectomy, or of not needing radiation or chemo,” said Gralow. “In some of these cases, the outcome would be the same—no death—but the impact on the patient would be different. You can’t discount the benefits of not needing chemo or of keeping your breast by not needing a mastectomy.”
Gralow also took issue with the Canadian study’s finding that screening mammography is leading to over-diagnosis and overtreatment, that is, detecting cancers that, if unfound and untreated, would not have been fatal. Few people, she said, would disagree with removing a funny-looking mole on the skin or a colon polyp, even if chances are high they aren’t cancerous.
Additionally, she pointed out that a study of mammography done in the 1980s is also less relevant today because the technology has improved.
“The type of mammography we did in the 1980s was plain film,” Gralow said. “Now we do digital and it’s much better for finding cancers and requiring fewer biopsies for things that are benign.”
That said, both researchers acknowledged that some breast cancer groups may have overly raised expectations of mammograms in their efforts to convince women to go through an uncomfortable screening once a year.
Studies have shown, for example, that mammography misses about 25 percent of cancers in women in their 40s and about 10 percent in older women, Gralow said. Dense breast tissue, which is more common in younger women but can be found in older women too, can hide cancers, and fast-growing tumors can develop in the period between mammograms.
For these reasons, women should be mindful of how their breasts typically feel and look and check out any changes.
“If you feel something or notice something different, go in and get it checked,” Gralow said. “I have patients who say, ‘I just had a normal mammogram so this funny lump I have is probably nothing.’ If you get a lump later, you should check it out.”
Dr. Anne McTiernan of Fred Hutch’s Public Health Services suggests tips to prevent breast cancer, including maintaining a healthy weight, keeping active and avoiding hormone replacement therapy. She recommends that women talk with their doctors to decide what type of screening they need and how often they need it, and that women at high risk of breast cancer—including women with the BRCA gene, a family history or a history of benign breast disease—ask about additional screenings.
Follow Mary Engel on Twitter @Engel140.