Clinical Edge

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Evaluating Mammography Screening Effectiveness

N Engl J Med; 2016 Oct 13; Welch, Prorok, et al

Publish date:

After the introduction of screening mammography and the decline in the rate of the detection of large tumors, the detection of breast cancer tumors that were small increased, with reduction in breast cancer mortality predominantly the result of improved systemic therapy, a recent study found. Researchers used data from the Surveillance, Epidemiology, and End Results (SEER) program from 1975 to 2012 to calculate tumor size distribution and size-specific incidence of breast cancer among women aged ≥40 years. They found:

  • The proportion of detected breast tumors that were small increased from 36% to 68% while the proportion of detected tumors that were large decreased from 64% to 32%, after the advent of screening mammography.
  • This trend was the result of a substantial increase in the detection of small tumors.
  • Women were more likely to have breast cancer that was overdiagnosed than to have earlier detection of a tumor that was destined to become large.
  • The potential of screening to lower breast cancer mortality is reflected in the declining incidence of larger tumors.

Citation:

Welch HG, Prorok PC, O’Malley AJ, Kramer BS. Breast-cancer tumor size, overdiagnosis, and mammography screening effectiveness. N Engl J Med. 2016;375:1438-47. doi:10.1056/NEJMoa1600249.

Commentary:

Breast cancer is the most common cancer in US women and the second leading cause of cancer death. The USPSTF recommends biennial screening mammography for:

  • Women aged 50 to 74 years.
  • The decision to start screening mammography in women prior to age 50 years should be an individual one.
  • They also conclude that the current evidence is insufficient to assess the balance of benefits and harms of screening mammography in women aged 75 years or older.1

The recommendations of the American Cancer Society are somewhat different:

  • Women with an average risk of breast cancer should undergo regular screening mammography starting at age 45 years (strong recommendation).
  • Women aged 45 to 54 years should be screened annually (qualified recommendation).
  • Women 55 years and older should transition to biennial screening or have the opportunity to continue screening annually (qualified recommendation).
  • Women should have the opportunity to begin annual screening between the ages of 40 and 44 years (qualified recommendation).
  • Women should continue screening mammography as long as their overall health is good and they have a life expectancy of 10 years or longer.2

While the present study raises provocative questions, for now the recommendations remain as listed above. —Neil Skolnik, MD

  1. US Preventive Services Task Force. Breast Cancer: Screening. January 2016. https://www.uspreventiveservicestaskforce.org/Page/Document/UpdateSummaryFinal/breast-cancer-screening1?ds=1&s=Breast%20cancer%20screening. Accessed October 24, 2016.

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