Results Summary

What was the research about?

Doctors use imaging tests, alone or together, to detect breast cancer, including:

  • Digital mammogram, or DM, a 2D x-ray
  • Tomosynthesis, or DBT, a 3D x-ray
  • Magnetic resonance imaging, or MRI, which uses magnetic fields and radio waves to take pictures

These tests may differ in their benefits, like detecting cancer early; their harms, like false alarms; and their failures, like missing a cancer diagnosis.

In this project, the research team did two studies to compare imaging tests:

  • Study 1 compared DM versus DBT for breast cancer screening. It also compared DM or DBT alone versus DM or DBT plus MRI.
  • Study 2 compared having or not having an MRI before surgery for women with breast cancer.

For both studies, the research team looked at women with dense and non-dense breasts separately. Having dense breasts is common but makes it hard to see cancer on DM and DBT and increases breast cancer risk.

What were the results?

Women with dense breasts.

Study 1. DBT and DM didn’t differ in study outcomes, except women who had DM had lower worry about cancer.

Compared with DM or DBT alone, women who also had an MRI had:

  • Higher benefits
  • Higher harms
  • No difference in failures
  • More confidence in screening
  • More worry about cancer

Study 2. Compared to women with breast cancer who didn’t have an MRI before surgery, women who had one had:

  • Higher rates of additional breast cancer detected at six months but not at three years
  • More worry about cancer
  • No difference in decision quality, conflict, or regret

Women with non-dense breasts.

Study 1. Compared with DM, screening with DBT had:

  • Higher benefits
  • Lower harms
  • No difference in failures or in women’s confidence in screening or worry about cancer

Compared with DM or DBT alone, women who also had an MRI had:

  • Higher benefits
  • Higher harms
  • No difference in failures
  • More confidence in screening
  • More worry about cancer

Study 2. Compared to women with breast cancer who didn’t have an MRI before surgery, those who had one had:

  • Higher rates of additional breast cancer detected at six months but not at three years
  • Improved decision quality
  • No difference in decision conflict and regret or worry about cancer

What did the research team do?

The research team used data from seven breast imaging registries across the United States. Study 1 included data from 504,150 women who had 1,377,902 screening tests. Study 2 included data from 20,383 women with breast cancer.

Subsets of 2,329 women from study 1 and 957 women from study 2 completed surveys on screening confidence, cancer worry, and decision quality.

Women who had breast cancer, doctors, and advocates gave input during the studies.

What were the limits of the study?

The research team didn’t assign women by chance to the imaging tests. Differences among women, such as reasons for screening, could have affected study outcomes.

Future research could look at other outcomes of imaging tests among women with dense and non-dense breasts.

How can people use the results?

Doctors and women can use the results when considering imaging tests for breast cancer.

Final Research Report

View this project's final research report.

Journal Citations

Results of This Project

Related Journal Citations

Peer-Review Summary

Peer review of PCORI-funded research helps make sure the report presents complete, balanced, and useful information about the research. It also assesses how the project addressed PCORI’s Methodology Standards. During peer review, experts read a draft report of the research and provide comments about the report. These experts may include a scientist focused on the research topic, a specialist in research methods, a patient or caregiver, and a healthcare professional. These reviewers cannot have conflicts of interest with the study. 

The peer reviewers point out where the draft report may need revision. For example, they may suggest ways to improve descriptions of the conduct of the study or to clarify the connection between results and conclusions. Sometimes, awardees revise their draft reports twice or more to address all of the reviewers’ comments.   

Peer reviewers commented and the researchers made changes or provided responses. Those comments and responses included the following: 

  • The reviewers asked the researchers to provide their rationale for excluding breast cancer surveillance registries from some parts of the United States. The researchers explained that they did include all breast cancer registries in the United States but acknowledged that some parts of the country were not covered by such registries. They added a limitation to the report to acknowledge that their results might not generalize to those parts of the country not covered by a registry. 
  • The reviewers requested that the researchers discuss the patterns of missing mammography data in their study sample since the level of missingness appeared to be substantial and could affect study conclusions. The researchers provided more specific information about why some mammograms were missing, saying that they were not able to collect data from some of the clinical sites at certain times. Because the missing data did not seem to be related to the interventions, the researchers considered these mammograms missing at random. 
  • The reviewers noted that the analyses only accounted for clustering of patients within facilities, without consideration of clustering of procedures within patients and patients within providers. They asked the researchers to justify this approach. The researchers explained that they accounted for clustering in whichever way made the most sense for the study aim. In one aim they adjusted for correlations within matched groups while in other aims they used robust analytic techniques which could account for most of the clustering given that patients are typically clustered within providers and providers within clinics. 
  • The reviewers asked for more detail on the qualitative analyses in this project, and in particular asked the researchers to present some representative quotes and other data to support the themes the researchers identified in their qualitative work. The researchers added representative quotes for both the main research study focus groups and for the focus group that was part of their COVID-19 Enhancement study. 

Conflict of Interest Disclosures

Project Information

Diana L. Miglioretti, PhD
University of California, Davis
Comparative Effectiveness of Breast Cancer Screening and Diagnostic Evaluation by Extent of Breast Density

Key Dates

May 2016
March 2023

Study Registration Information


Has Results
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Intervention Strategy Intervention Strategies PCORI funds comparative clinical effectiveness research (CER) studies that compare two or more options or approaches to health care, or that compare different ways of delivering or receiving care. View Glossary
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Last updated: April 10, 2024