Women in their 40s continue to get routine mammograms, despite national guidelines recommending otherwise, according to new research performed at Johns Hopkins University.

In 2009, the U.S. Preventive Services Task Force (USPSTF) reviewed evidence and recommended that women ages 50-74 continue to receive mammograms every two years. But for women between 40 and 49 with no family history of breast cancer, the group recommended discussing the costs and benefits of routine mammography with a physician, and to make decisions on a case-by-case basis.

The researchers who performed the new Johns Hopkins study expected that, given the 2009 recommendations, fewer women in their 40s would undergo routine mammograms. However, their findings suggested otherwise.

Researchers found no change in the rate of mammography among younger women, despite revised recommendations following the 2009 study.

"Patients - and likely their providers - appear hesitant to change their behavior, even in light of evidence that routine screening in younger women carries substantial risk of false positives and unnecessary further imaging and biopsies," said Lauren Block, clinical fellow in the Division of General Internal Medicine at the Johns Hopkins University School of Medicine. "Women have been bombarded with the message 'mammograms save lives,' so they want them no matter what."

The study, published online in the Journal of General Internal Medicine, found that the health results of mammography for women in their 40s were mixed.

Rates of breast cancer detection are increased by routine mammography, but so are rates of false positives, especially in younger women. False positives can lead to overdiagnosis and unnecessary treatment, including biopsies, lumpectomies, and mastectomies, as well as radiation and potentially toxic drugs.

False positives also lead to psychological trauma, for instance, in cases of cancers that are overtreated, even if they would never have become dangerous.

Mammographies for younger women have been shown to increase cancer detection rates, but reduce mortality by only a small percentage.

The original change in USPSTF guidelines recommended more strongly against routine screening for women in their 40s. However, a political and advocacy group backlash resulted in compromised language counseling individual decision-making by patients and physicians.

The American Cancer Society continues to recommend yearly mammography for women starting at age 40.

Mammographies are still recommended for older women, and for women in their 40s with a family history of breast cancer.

Block said that the high rate of mammography screening for women in their 40s may be related to their source of funding. Insurance companies pay for routine mammographies, making them more attractive to patients.

The study was conducted using data from Behavioral Risk Factor Surveillance System surveys administered in 2006, 2008, and 2010 by state health departments throughout the country. 484,296 women ages 40 to 74 answered survey qustions. In 2006 and 2008, 53 percent of women in their 40s reported having a mammogram in the past year, compared to 65 percent of women ages 50 to 74. In 2010, following the new recommendations, 52 percent of younger women and 62 percent of older women reported having a mammogram.

The USPSTF recommendations say that there is no benefit to screenings for women at normal risk of breast cancer over the age of 75.

In conversations with her patients, Block found that some women in their 40s are reluctant to change their mammography screening, and some are relieved that they can postpone screening until their 50s.

"Breast cancer gets so much attention in the media and in society in general, despite cardiovascular disease being by far the number one killer in women. Everyone wants to feel as though they are preventing breast cancer," Block said. "You hear one anecdotal story about someone in their 40s who found cancer during a mammogram and did really well with treatment and that's enough to fly in the face of any other facts that are out there. Women want the test."