Mammograms are x-ray exams of the breasts that are used for women who are asymptomatic, those women who appear normal with no breast problems. But U.S. researchers have found breast cancer screening may not lead to fewer deaths but may lead to overdiagnosis instead, according to Huffington Post.

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Researchers report that In some 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, ABS-CBN News reports.

Charles Harding, the study's lead author from Seattle, Washington, cautioned women saying, "The mortality results that we observed are far from definitive," He added, "That most dramatic finding of our study is the immediately evident, and substantial evidence of breast cancer overdiagnosis."

According to National Cancer Institute, approximately 230,000 women in the U.S. are diagnosed with breast cancer each year.

The government-backed U.S. Preventive Services Task Force suggested that average-risk women should be tested and have mammogram screening every other year between the ages 50 and 74. For women below the age of 50, they, too, are allowed to undergo screening.

For the new study, researchers analyzed breast cancer screenings, cancer diagnoses, tumor characteristics and deaths in the U.S.

The data was gathered from an ecological study of 16 million women who reported to Surveillance, Epidemiology and End Results cancer registries 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.

More than 50,000 of the women were diagnosed with breast cancer and they were re-examined every so often for the next 10 years, Daily Time Gazette reports. 

The results of their study, which have been published in the journal JAMA Internal Medicine, showed that the number of breast cancer patients being diagnosed increased with the number of screenings, but the number of breast cancer deaths over the next 10 years remained the same.

According to Huffington Post, a 10 percentage point increase in breast cancer screenings was tied to a 16 percent increase in breast cancer diagnosis, but the number of screening mammograms performed did not affect the number of breast cancer deaths.

Researchers found that mammograms screening may be associated to overdiagnosis of "small, indolent or regressive tumors" because they mainly catch smaller tumors.

Harding said, "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." 

Harding believes that their study has the potential of raising awareness and answering important questions about the benefits of mammography screening. However, he also admitted that their findings are quite tentative because the data they managed to obtain have minor inconsistencies.He added that more research is needed to fully understand the results.

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, ABS-CBN News reports.

Dr. Joann Elmore and Ruth Etzioni of the University of Washington in Seattle agreed on the researchers statement that the study's results are limited by the potential of ecological bias.

They gave an example, that there is no way to know if the women who received the mammograms screening were the same women who went on to be diagnosed with the disease.

"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.

TagsMammograms, Screening, Diagnosis, breast cancer, Study, Disease