More than a quarter-century after women were told to get annual mammograms beginning at age 40, researchers still don’t agree on whether the screening X-rays significantly reduce a younger woman’s risk of dying from breast cancer. Studies have produced conflicting results.
A new analysis from Massachusetts General Hospital researchers suggests that mammograms prevent breast cancer deaths in women in their 40s by detecting some cancers in an earlier, more curable stage than cancers detected in women who don’t get screened.
At first blush, the findings published online in the journal Cancer, seem to make a strong case in favor of mammography screening for younger women. But there are some serious limitations in the study design that cast doubt on the findings.
The resesarchers analyzed 609 breast cancer deaths that occured at hospitals in the Partners HealthCare system between 1990 and 1999 and found that more than 70 percent of the deaths occurred in the 20 percent of the women who weren’t getting regular mammograms.
The average age of the women who died from breast cancer was 49, leading the researchers to conclude that screening these women in their 40s might have caught the cancers early enough to have prevented some of these deaths.
“I don’t know the best time to start, but I would argue that at least starting before age 50 has the potential to reduce breast cancer mortality in younger women,” said study co-author Dr. Blake Cady, a professor of surgery (emeritus) at Harvard Medical School. These cancers tend to faster growing, more aggressive, and more likely to kill than cancers found in older women -- though sometimes they’re not found quickly enough by mammograms.
About 30 percent of the women in the study who died of breast cancer were diagnosed between ages 40 and 49. On the other hand, 20 percent of those who died were diagnosed in their 30s, so does this mean we should screen women under 40 as well?
Cady admitted that screening recommendations largely relied on arbitrary age cut-offs and that the exact age where women reap enough benefits from the screening to outweigh the risks remains an “open question.”
While most mammography researchers would agree with that assessment, some say the latest study is too flawed to be taken very seriously.
Dr. Gil Welch, a professor of medicine at the Dartmouth Institute for Health Policy & Clinical Practice, said the study is “telling us half the story” because it examined only women who were diagnosed with breast cancer, rather than sampling a general population of women in their 40s to see whether those who were screened were more likely to die of breast cancer.
Welch published a controversial analysis last year in which he calculated that mammogram recommendations over the past three decades had led to an overdiagnosis of breast cancer in more than 1 million women, causing them to be treated for nonaggressive cancers that would have never gone on to become life threatening.
Cady said the new study was designed to compare only women who died of breast cancer with those who were diagnosed with breast cancer and didn’t die of the disease after an average of 13 years of followup. He conceded that the benefits seen in the screened women don’t necessarily apply to a larger population of women who might or might not have breast cancer.
Welch pointed out another major limitation of the study: It didn’t account for possible differences between women who chose to have regular mammograms and those who skipped the screenings. Previous studies suggest that women who regularly get mammography tend to be higher income, better educated, healthier overall, and have better access to health care, which could lead them to make a doctor’s appointment the minute they feel a breast lump.
Women who aren’t regularly screeened may be diagnosed and treated for more advanced cancers simply because they avoid going to the doctor.
The way to figure out whether screening helps prevent deaths is by conducting controlled clinical trials where women are randomly assigned to have screening beginning at age 40. “That’s been done in nine studies, involving over a half-million women,” Welch said, “and it looks like screening [starting at age 40] lowers cancer mortality somewhere between 0 and 25 percent.”
He said researchers still don’t know the true effect of mammogram screening in younger women. “I believe there is some benefit, but it is small.”