Study: Mammography Screening Every Two Years Does Not Increase Risk of Advanced Stage Tumors

A study appearing early online in JAMA Internal Medicine (formerly Archives of Internal Medicine) suggests that women  50 to 74 years old who undergo biennial screening have a similar risk of advanced-stage disease and a lower cumulative risk of false-positive results than those who get mammograms annually.

The study, by Karla Kerlikowske, M.D., of the University of California, San Francisco, and colleagues sought to determine whether the benefits and risks of screening mammography differ according to age, breast density, and the use of hormone therapy (HT). The authors found that biennial vs. annual mammography for women ages 50 to 74 was not associated with an increased risk of advanced-stage or large-size tumors regardless of a women’s breast density or HT use. However, the results indicate that among women ages 40 to 49 with extremely dense breasts, biennial mammography vs. annual was associated with an increased risk of advanced-stage cancer and large tumors.

The authors conclude that women aged 50 to 74 years can undergo biennial rather than annual mammography and that women aged 40 to 49 years with extremely dense breasts who choose to undergo mammography should consider annual screening to decrease the risk of advanced-stage disease but should be informed that annual screening leads to a high cumulative probability of a false-positive result.

Below are comments from Robert A. Smith, Ph.D., American Cancer Society director of cancer screening.Rsmith2010jpg

“This new study adds to mounting data that older women can be screened at a wider interval, and that a shorter interval does increase the false positive rate without much additional advantage. The fact is, screening guidelines tailored to individual characteristics really need a more precise tool than age alone (example: ages 40 to 49 versus 50 and above). The question for individual women becomes when to move screening from an annual procedure to every 2 years, and which women are most likely to benefit from continuing with annual screening. We may see a time when that age is moved from the current, age 50, to something like age 55, an age when most women have passed through menopause.

“The benefits of a shorter interval for most women in their 40s is fairly well established. The screening interval should probably be shorter for women with very dense breasts, women with a family history of breast cancer, and women who are taking menopausal hormone therapy.

“What has been shown consistently is that for women in their 40s, the risk of a cancer developing in between mammograms, what we call an interval cancer, is much higher in the first 6 to 18 months after a normal mammogram than it is for women over 50. It may very well be that this higher rate is attributable mostly to breast density, and if so, then perhaps some women in their forties could begin screening at a wider interval based on density. But we’re not there yet; we would need to do quite a bit of analysis to figure out this complicated equation. We cannot say with certainty what level of density might benefit from annual versus longer screening intervals, which may be 18 months or two years.

“Also we are moving towards a day when we will have personalized screening. Some women based on age and other risk factors may be told to get a mammogram every two or perhaps three year; others will be told to get one annually; some may be told to get mammography or MRI imaging even more frequently. We have not reached that day.”

“Until then, if we advise a woman that it is safe to follow a less aggressive preventive health regimen, like waiting longer between mammography screenings, you want to be very sure you are giving her the right advice. So far, surveys show that women prefer safety, and are more willing to live with the consequences of a false positive than risk a missed tumor.

“The American Cancer Society continually reviews emerging data as we create and update our own screening guideline. This study and many others will be included in the evidence review a panel of independent experts will review as a routine part of that work.”

About David Sampson

I am the director of medical and scientific communications for the American Cancer Society national home office.
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