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Study: Mammograms Can Be Less Frequent and Later

November 17, 2009 – A new research paper, led by Georgetown’s Dr. Jeanne Mandelblatt, suggests that biennial mammograms of average-risk women between the ages of 50 and 74 achieves most of the benefits and less harm than the yearly screenings for breast cancer.

The findings represent a unanimous consensus of six independent research groups from various academic institutions, including Georgetown, that were published in the Nov. 17 issue of Annals of Internal Medicine.

Researchers from the Cancer Intervention and Surveillance Modeling Network (CISNET) used independent models to examine 20 screening strategies with different starting and stopping ages and intervals. Modeling estimates the lifetime impact or the benefits and harms of breast cancer screening mammography.

“It’s reassuring that all CISNET modeling groups came to the same conclusion even when applying different models to these data,” said Mandelblatt, associate director of population sciences at Georgetown’s Lombardi Comprehensive Cancer Center.

The CISNET analysis was also one of many sources of evidence that the U.S. Preventive Services Task Force relied upon to develop new guidelines for mammograms announced on Nov. 17.

“While the [CISNET] findings represent a comprehensive review of existing data, decisions about the best screening strategy depend on individual and public health goals, resources and tolerance for false-positive mammograms, unnecessary biopsies and over-diagnosis,” Mandelblatt,added.

Avoiding False-Positive Results

Model results confirmed that mammography saves lives, but Mandelblatt believes there are smaller overall benefits from starting screenings before age 50 because few women develop breast cancer in younger age groups.

Screening younger women is accompanied by a large number of false-positive mammograms, she said.

“This can lead to stress for women and unnecessary biopsies,” she explained. “We need more research to understand how to tailor screening by individual risk.”

The CISNET analysis shows that screening every other year maintains almost all of the benefit – an average of 81 percent – of annual screening with almost half the number of false-positives. Compared with no screening, mammography screening every other year from ages 50 to 69 achieves a median reduction in breast cancer mortality of 16.5 percent over a lifetime.

If screenings begin at age 40 vs. age 50 and are performed every other year, she says, there is a median mortality reduction of 19.5 percent, which adds up to an additional one woman per 1,000.

Biennial Benefits Seen

Mandelblatt says the benefits of biennial screening are consistent with what is known about breast cancer’s biology. Most breast cancer tumors grow slowly and the size increases with age, so there is little loss in survival benefit across the population for screening annually versus every other year.

For women with aggressive, faster-growing tumors, annual screening is unlikely to affect survival, according to Mandelblatt. For these women, different approaches may be needed and that remains an important area of ongoing research.

“These modeling data represent an average finding regarding the population of women, so it can’t be emphasized enough that women need to talk to their health care provider for a screening program that is best for them,” Mandelblatt added.

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