Women in their 40s continue to undergo routine breast cancer screenings despite national guidelines recommending otherwise, according to new Johns Hopkins University research.

In 2009, the U.S. Preventive Services Task Force (USPSTF) sifted through the evidence and recommended that while women ages 50 to 74 should continue to undergo mammograms every two years, those between the ages of 40 and 49 without a family history of breast cancer should discuss the risks and benefits of routine screening mammography with their physicians to make individual decisions.

As a result of the altered recommendations, Dr. Lauren D. Block, a clinical fellow in the Division of General Internal Medicine at the Johns Hopkins University School of Medicine in Baltimore, Md., and her colleagues expected to find fewer women in their 40s getting routine mammograms. Instead, they found no impact on mammography rates among younger women.

"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," says Block, leader of a study published online in the Journal of General Internal Medicine. "Women have been bombarded with the message 'mammograms save lives,' so they want them no matter what."

That research has shown that mammography's impact on younger women is mixed at best: Routine screening increases rates of detecting cancer in young women, but reduces mortality risk by a very small percentage.

It is more likely, studies show, to result in over-diagnosis, and unnecessary treatment, including biopsies, lumpectomies, and mastectomies, and weeks of radiation and potentially toxic drugs. False positives result in avoidable procedures and psychological trauma. Many of the cancers detected probably will never be dangerous, but are treated aggressively.

Among older women, screening mammograms are recommended because breast cancer, like most cancer, is a disease of aging, and a woman's risk of breast cancer increases as she grows older.

The original USPSTF guideline change recommended more forcefully against routine screening for women in their 40s, but a political and advocacy group backlash resulted in compromise language that counseled individual decision-making by patients and physicians. The American Cancer Society continues to recommend yearly mammography for women starting at age 40.

Moreover, Block says, insurance companies continue to pay for routine mammograms for women in their 40s—a likely reason for the persistently high rate of screening.

Block and her colleagues analyzed mammogram use data from Behavioral Risk Factor Surveillance System surveys administered in 2006, 2008, and 2010 by state health departments nationwide. Data from 484,296 women ages 40 to 74 were collected.

Among women in their 40s, 53 percent reported having a mammogram in the past year in 2006 and 2008, compared with 65 percent of women ages 50 to 74. In 2010, after the new recommendations had been in effect, 52 percent of younger women and 62 percent of older women reported having a mammogram. The USPSTF recommendations also say there is no benefit to screening women at normal risk of breast cancer over the age of 75.

Block says she sees the same reluctance among her 40-something patients to change course on mammography when she has the conversations about the pros and cons.

Some of her patients are relieved that they can postpone mammography until age 50. Many more, however, want to continue being screened.