(Updates with comment from study author Charles Harding throughout story.)
(Reuters Health) - Breast cancer screenings may not lead to fewer deaths but may lead to overdiagnosis, U.S. researchers suggest.
In areas of the U.S. with high levels of screening, more tumors were diagnosed - but breast cancer death rates were no lower than in areas with fewer screenings, researchers report.
"The mortality results that we observed are far from definitive," cautioned Charles Harding, the study's lead author from Seattle, Washington.
"The most dramatic finding of our study is the immediately evident - and substantial - evidence of breast cancer overdiagnosis," he told Reuters Health in an email.
Each year, about 230,000 U.S. women are newly diagnosed with breast cancer, according to the National Cancer Institute.
While screening guidelines vary, the government-backed U.S. Preventive Services Task Force says average-risk women should have mammograms every other year between ages 50 and 74. Getting screened before age 50 should be an individual decision, according to the Task Force.
For the new study, researchers analyzed breast cancer screenings, cancer diagnoses, tumor characteristics and deaths in 547 U.S. counties.
The data came from nearly 16 million women living in those counties in 2000. All were at least 40 years old. The percentage who had screening mammograms ranged from 39 percent to 78 percent, depending on where they lived.
Overall, more than 53,000 of the women were diagnosed with breast cancer in 2000.
The researchers report in JAMA Internal Medicine that the number of breast cancer diagnoses rose with the number of screenings, but the amount of breast cancer deaths over the next 10 years remained the same.
Overall, a 10 percentage point increase in breast cancer screenings was tied to a 16 percent increase in breast cancer diagnoses.
The number of screening mammograms performed did not affect the number of breast cancer deaths, however.
Most of the additional cancers detected on screening were small tumors. There wasn't an increase in diagnosis of large - and presumably more advanced - tumors.
The findings suggest breast cancer screenings lead to overdiagnosis because they mainly catch smaller tumors, the researchers say.
"We were troubled that we did not see evidence of a mortality benefit from screening, especially because there was no relationship between screening and advanced-stage cancer, either," Harding said.
"However, our findings are quite tentative for mortality because the data are very noisy," he added. "We feel that our study raises important questions about the benefits of mammography screening, but it certainly does not answer them."
More research is needed, he said.
The researchers also warn in their paper that their findings may be limited by so-called ecological bias, which can occur when assumptions are made about individuals from data of a large group.
Dr. Joann Elmore and Ruth Etzioni of the University of Washington in Seattle agree in an editorial that the study's results are limited by the potential of ecological bias.
For example, there is no way to know if the women who received the mammograms were the same women who went on to be diagnosed with the disease, they write.
Also, Elmore and Etzioni caution, other unmeasured factors may account for the lack of difference in breast cancer deaths.
"Prior ecological studies of mammography conducted at the larger state level with a wider range of mammography frequencies showed a decline in breast cancer mortality associated with more screening," Elmore and Etzioni added.
SOURCE: http://bit.ly/1IZB2nH and http://bit.ly/1KISFwu JAMA Internal Medicine, online July 6, 2015.
Our 2024 Coverage Needs You
It's Another Trump-Biden Showdown — And We Need Your Help
The Future Of Democracy Is At Stake
Our 2024 Coverage Needs You
Your Loyalty Means The World To Us
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Contribute as little as $2 to keep our news free for all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
The 2024 election is heating up, and women's rights, health care, voting rights, and the very future of democracy are all at stake. Donald Trump will face Joe Biden in the most consequential vote of our time. And HuffPost will be there, covering every twist and turn. America's future hangs in the balance. Would you consider contributing to support our journalism and keep it free for all during this critical season?
HuffPost believes news should be accessible to everyone, regardless of their ability to pay for it. We rely on readers like you to help fund our work. Any contribution you can make — even as little as $2 — goes directly toward supporting the impactful journalism that we will continue to produce this year. Thank you for being part of our story.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
It's official: Donald Trump will face Joe Biden this fall in the presidential election. As we face the most consequential presidential election of our time, HuffPost is committed to bringing you up-to-date, accurate news about the 2024 race. While other outlets have retreated behind paywalls, you can trust our news will stay free.
But we can't do it without your help. Reader funding is one of the key ways we support our newsroom. Would you consider making a donation to help fund our news during this critical time? Your contributions are vital to supporting a free press.
Contribute as little as $2 to keep our journalism free and accessible to all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Contribute as little as $2 to keep our news free for all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. Would you consider becoming a regular HuffPost contributor?
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. If circumstances have changed since you last contributed, we hope you'll consider contributing to HuffPost once more.
Support HuffPostAlready contributed? Log in to hide these messages.