Breast Cancer: Are Yearly Mammograms Worthwhile?
Estimating Overdiagnosis of Breast Cancer continued...
Researchers think that means that many early breast cancers -- perhaps as many as half of all cancers detected by mammograms -- are probably harmless and are being “overdiagnosed.”
Overdiagnosis is “the diagnosis of nothing, or something that is nothing,” says Bleyer.
“Whatever is found would never have created a problem during that person’s life. They wouldn’t have known about it otherwise,” he says.
The problem is that doctors can’t tell which early cancers may be harmless and which may become life-threatening. So once the call is made, patients are offered treatment including surgery, chemotherapy, and radiation.
“If we had a way to better distinguish within that diagnosis which cancers were likely to cause a problem, we would save a lot of women from unnecessary treatment,” says Sharon Giordano, MD. Giordano is a breast medical oncologist at MD Anderson Cancer Center in Houston. She was not involved in the research.
Does Early Detection Save Lives?
Researchers also looked at whether or not early detection with mammograms was saving lives.
Over the period of the study, death rates from breast cancer in women 40 years or older dropped by 28%, a substantial decline.
But breast cancer death rates dropped even more (42%) among women under age 40, a group that doesn’t routinely get screening mammograms.
“We are left to conclude, as others have, that the good news in breast cancer -- decreasing mortality -- must largely be the result of improved treatment, not screening,” the researchers write.
This isn’t the first study to flag the harms of overdiagnosis tied to mammograms. Ten other studies conducted in Europe and Australia have estimated that somewhere between 10% and 47% of all breast cancers detected in those countries are unnecessarily treated.
Certain cautions apply.
The first is that it’s not possible to directly count cases of overdiagnosis. Studies that try to have to rely on estimates. Those estimates are always subject to errors and biases.
The second caveat is that the study results don’t apply to everyone.
Women at higher risk of cancer because they have a family history or because they carry genes for the disease “really have nothing to do with this,” Bleyer says. “They are in a completely different category and they do need to be detected as early as possible, because they get a worse kind of cancer and they get it earlier in life.”