Clinical Edge

Summaries of Must-Read Clinical Literature, Guidelines, and FDA Actions

Evaluating Mammography Screening Effectiveness

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

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.


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.