Regular Screening Increases Detection of Early-Stage Cancers, but Not Later-Stage Disease

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A large U.S. study suggests that over the past 30 years, regular screening mammograms have found more early-stage breast cancer. Still, the results also suggest that mammograms don’t seem to have improved detection of more advanced-stage disease and may have overdiagnosed a large number of women.

Overdiagnosis means either:

  • a screening mammogram finds a suspicious area that would have been eventually diagnosed as cancer by other means, without any effect on prognosis
  • a screening mammogram finds a suspicious area that never would have affected a woman’s health if it hadn’t been found or treated

The study was published in the Nov. 22, 2012 issue of the New England Journal of Medicine. Read the abstract of “Effect of Three Decades of Screening Mammography on Breast-Cancer Incidence.”

The researchers looked at information on breast cancer in SEER, a large U.S. National Institutes of Health database. Using that information and their assumptions about how the incidence of breast cancer changed over time, they estimated how many women 40 and older would be diagnosed with breast cancer in two time periods: 1976 to 1978 (early period) and 2006 to 2008 (late period).

Their results showed that annually there were:

  • 7 cases of DCIS (ductal carcinoma in situ) per 100,000 women in the early period compared to 56 cases of DCIS per 100,000 women in the late period
  • 105 cases of early-stage breast cancer per 100,000 women in the early period and 178 cases of early-stage cancer in the late period
  • 85 cases of more advanced-stage breast cancer per 100,000 women in the early period and 78 cases of more advanced-stage breast cancer in the late period
  • 17 cases of metastatic breast cancer (cancer that has spread to parts of the body away from the breast) in both the early and the late period

This works out to be about 122 extra cases of early-stage breast cancer being diagnosed in the late period compared to the early period. In addition, there were eight fewer cases of more advanced stage breast cancer diagnosed in the late period compared to the early period.

According to the researchers, this would amount to about 70,000 women being overdiagnosed in 2008.

It’s important to know that the results of this study are controversial. Many doctors believe that the researchers’ assumptions about how the incidence of breast cancer changed over time were wrong and led to flawed results.

In the debate about the value of breast cancer screening and when screening should begin, overdiagnosis is an issue that raises some concerns. Overdiagnosis leads to possibly unnecessary tests and treatment, as well as the associated physical, emotional, and economic consequences. Doctors continue to work on ways to improve the quality of breast cancer screening programs and minimize the risk of overdiagnosis. More work needs to be done.

Still, the value of breast cancer screening must be weighed against the many timely diagnoses -- and lives saved -- that come from regular screening. Taken together, the evidence strongly suggests that breast cancer screening starting at age 40:

  • leads to diagnoses of breast cancer at earlier, more treatable stages
  • means better prognoses for women diagnosed -- and lives saved

Despite the evidence and current mammogram guidelines, many women age 40 to 49 don't get regular screening mammograms.

If you're 40 or older and have an average risk of breast cancer, yearly screening mammograms should be part of your healthcare. If your breast cancer risk is higher than average, you may want to talk to your doctor about a more aggressive breast cancer screening plan that makes the most sense for your particular situation.

There's only one of you and you deserve the best care possible. Don't let any obstacles get in the way of regular screening mammograms:

  • If you're worried about cost, talk to your doctor, a local hospital social worker, or staff members at a mammogram center. Ask about free programs in your area.
  • If you're having problems scheduling a mammogram, call the National Cancer Institute (800-4-CANCER) or the American College of Radiology (800-227-5463) to find certified mammogram providers near you.
  • If you find mammograms painful, ask the mammography center staff members how the experience can be as easy and as comfortable as possible for you.

For more information on mammograms and other tests to detect breast cancer, visit the Breastcancer.org Breast Cancer Tests: Screening, Diagnosis, and Monitoring pages.

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