A new review of 100,000 women age 50 and older suggests routine mammograms may be doing more harm than good.
When taking into account the frequency of false positives (a diagnosis of cancer when there was none) and unnecessary surgery, the risk of breast cancer screening offsets the benefits, British researchers reported Thursday in BMJ.
"The default is to assume that screening must be good; catching something early must be good," said James Raftery, professor of health technology assessment at the University of Southampton, U.K., and lead author of the review. "But if a woman has an unnecessary mastectomy, or chemotherapy or radiation, that's a tragedy."
It's estimated that for one woman's life to be saved, 2,000 women have to be screened, leading to 200 false positives and 10 unnecessary surgeries.
To systematically weigh the risks and benefits of breast cancer screening, Raftery and research fellow Maria Chorozoglou reviewed previously published data in terms of quality adjusted life years -- a measurement that combines life years gained from screening with losses of quality of life from anxiety-provoking false positives and invasive surgery.
In the 10 years after screening, quality adjusted life years were a net negative, suggesting screening did more harm than good. Only after 20 years did the benefits start to mitigate the risks.
"It's difficult to balance the gain of one life against 200 false positives and 10 unnecessary surgeries," said Raftery. "But breast cancer screening was introduced because it was assumed to benefit women's health overall. And the side effects are pretty damn serious."
The alternative is watchful waiting: delaying treatment until it's clear whether a lump is truly a life-threatening tumor. But for woman faced with the words, "breast cancer," watchful waiting is easier said than done.
"When you have something termed 'cancer,' logical thinking seems to go out the window," said Dr. Mark Scholz, oncologist and author of the book "Invasion of the Prostate Snatchers."
Prostate cancer screening, like mammography, has its limitations. And many men risk impotence and incontinence for prostate surgery that might not be necessary.
"I'm a believer in screening," said Scholz. "But when you have an imperfect tool that helps a little but doesn't give a clear-cut answer, you need the back-up of a smart doctor and a well-educated patient."
Breast cancer screening guidelines have been the topic of debate over the past year. One study suggested routine mammograms can save lives for women over 40. Another found that mammography only led to a 10 percent reduction in mortality.
"In my opinion, the benefits far outweigh the potential harms, and screening should be performed annually starting at age 40 for women at average risk for breast cancer," Dr. Carol Lee, chairwoman of the American College of Radiology's Breast Imaging Commission, said in response to the two studies.
The U.S. Preventive Services Task Force recommends biennial mammograms for women aged 50 to 74.
According to a recent Gallup survey, 58 percent of Americans are satisfied with the current level of screening and 31 percent wish there was more. A mere 7 percent think there's too much.
"We need a lot more education," said Scholz of the risks of cancer screening, "for both patients and doctors."
But the best way to cut back on false positives and unnecessary surgeries, said Scholz, is to improve the accuracy of screening tests.
"There's going to come a day when there's better technology available," he said. "That's going to make the biggest difference."
In the meantime, the only way to truly know whether breast cancer screening causes more harm than good is to conduct a clinical trial in which women are randomly assigned to either have treatment based on the screening results or watch and wait.
"That would be almost impossible," said Scholz, believing few women would sign on. "But I would much rather have imperfect information [like the information from studies like Raftery's] than no information at all."
While large studies shed light on the benefits and risks of screening overall, experts stress that each patient is different. The picture is further complicated by the tendency of the 10 in 2,000 women who have unnecessary surgery just to be glad they don't have cancer.
"All of them think their lives were saved," said Raftery.