For decades it mostly went unquestioned: Women without symptoms were advised to undergo routine mammograms to assure they were cancer-free, with the idea that detection of early-stage breast cancer would increase their chances of survival.
But a controversial study recently published in the New England Journal of Medicine concludes that women without symptoms who undergo screening and are diagnosed with breast cancer may experience more harm than good.
The observational study analyzed national statistics on breast cancer screening and incidence and death rates for a 30-year period, and it found that advances in breast cancer treatment are far more responsible for the decline in deaths than screening.
The study concludes that 1.3 million women have been overdiagnosed with early-stage breast cancer -- which the study defines as "the detection of a cancer that otherwise was never going to appear." Despite having no symptoms, women may be subjected to unnecessary radiation and hormonal treatments and even mastectomies.
PG graphic: Finding breast cancer (Click image for larger version)
The study has received criticism and support.
The New York Times Well blog, "Ignoring the Science of Mammograms," written by David H. Newman, describes the findings as "a bold claim for an observational study."
"There are countless reasons why conclusions from such studies are commonly fraught with error," states Dr. Newman, an emergency room physician in New York City. "What if, for instance, the lion's share of advanced cancers occurred among women without access to screening mammograms -- a fact often not available in health statistics? Or what if mammography successfully prevented a major increase in advanced cancers, leaving the health statistics unchanged?"
A study author, H. Gilbert Welch, a professor of medicine at the Dartmouth Institute for Health Policy & Clinical Practice at Dartmouth University, said the controversy was expected, although he said some criticisms are laughable. "This is a hot potato," he said. "There is probably no diagnostic or screening test promoted as aggressively as mammography. There is nothing like it, and people have engaged in the process [of being screened]."
But he said the study makes clear that the benefit of screening "is much smaller than people have been led to believe, and the harms are considerably larger."
Benefits are outweighed, he said, by the study's conclusions that 1.3 million women in the past 30 years -- 70,000 in 2008 alone or 31 percent of all breast cancers diagnosed that year -- were overdiagnosed, leading to unnecessary mastectomies or radiation and hormone treatments.
Diagnostic mammography for women who have symptoms, including detected lumps in their breasts, is recommended, Dr. Welch said, noting the importance of taking action when a woman has clear symptoms of breast cancer. "There is no debate about mammography" for that purpose, he said.
"Treatment has gotten a lot better. The better the treatment, the less important it becomes to find the disease early," said Dr. Welch who teamed with Archie Bleyer, the medical advisor to the Cancer Treatment Center at St. Charles Medical Center in Bend, Ore., to do the study.
One irony, he said, is that women without symptoms who are screened, diagnosed with early-stage breast cancer, then undergo treatment for what never would have become breast cancer, often mistakenly attribute their lack of breast cancer to the treatment.
Despite its findings, the study doesn't recommend against screening. "Women should recognize that our study does not answer the question, 'Should I be screened for breast cancer?' However, they can rest assured that the question has more than one right answer."
The researchers analyzed more than 30 years of data about early- and late-stage breast cancer incidence, mortality, screening rates, among other data. Successful screening, it says, must find actual breast cancer earlier, with earlier treatment resulting in improved survival rates versus what would occur if the cancer reached late stage. Late-stage disease has spread to other parts of the body.
But the study found breast cancer incidence to have been stable for decades, with the only increases related to those caused by hormone replacement therapies. If screening were successful, the researchers said, it would reveal a sizable increase in the diagnosis of early-stage cancer and reduction in late-stage cancers. Only the first effect was observed.
"Seventy percent of the population currently undergoes mammography screening, causing early-stage diagnoses of breast cancer to increase dramatically," Dr. Welch says in a YouTube video he produced to explain the research. "But that hasn't led to a decrease in late-stage cancer diagnosis."
From 1976 to 2008, the study says, there was little change in the breast cancer rate among women under 40, suggesting that the increase in early-stage incidence of breast cancer relates solely to screening. And yet the number of late-stage cancers hasn't declined significantly. The study says that indicates that screening doesn't meet a basic prerequisite for success.
"The rate of metastatic breast cancer has not changed at all, and this is the group that really would benefit from their time of diagnoses," Dr. Welch said in the video. "These are the type of cancers we would like to find early, but we're not.
"The rate at which American women present with metastatic breast cancer -- a stage that is extremely difficult to treat -- sadly appears not to have been affected by screening," his video states.
It also says the decline in deaths among women under age 40, who don't generally undergo screening, is about the same as those over 40 who do. The study says that indicates that screening has little to do with the decline in breast-cancer mortality.
Common medical opinion continues to support screening, despite its shortcomings. On www.cancer.gov, the National Cancer Institute leads the page on mammograms with: "Screening mammography can help reduce the number of deaths from breast cancer among women ages 40 to 70." It also notes the following: "Potential harms of screening mammography include false-negative results, false-positive results, overdiagnosis, overtreatment, and radiation exposure."
Nancy E. Davidson, director of the University of Pittsburgh Cancer Institute and UPMC CancerCenter and a breast cancer specialist, said the medical community "constantly is trying to figure out how to screen better" with an ongoing dialogue about the risks and benefits of screening women who have no symptoms of breast cancer.
The study "raises a concern we all have," she said. "I would love to have a perfect screening tool that would allow us to find the cancer that threatens the person's health early, before the woman is symptomatic. And we would love not to find cancers that will not be life-threatening."
"We need to refine our screening approach -- who we screen, how we screen and when we screen them," Dr. Davidson said. "We are working toward doing less for some people because they do not need it and more for others who potentially are at high risk."
But she said the 10 percent decline in breast cancer mortality that the study links to screening "is not a small number of people."
Dr. Davidson said her personal recommendations are similar to those of the U.S. Preventive Services Task Force, which says that women 50 to 74 should be screened every two years. She said women of that age, for sure, should have a mammogram at least once every two years. Her recommendations are consistent with many other medical experts and institutions although some do recommend mammography annually from age 40.
Women 40 to 49 years also should discuss screening with their physician, then decide for themselves whether to undergo the process, she said.
"Women feel whipped back and forth on the mammography front," Dr. Davidson said. "As always, a woman shouldn't do anything unilaterally. She should talk with her health-care provider and do what's best for her.
"When people read the story, I hope an asymptomatic woman going through screening mammography does not read it and say, 'I don't need to do this anymore,' " she said. "Use it for discussion and think through the pros and cons of screening."