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Breast cancer screening and new treatments were associated with a large reduction in mortality from the disease over the past 45 years, according to results from a simulation model-based study.

Using four models, the combination of screening, stage I to III disease treatment, and metastatic disease treatment was associated with a 58% reduction in breast cancer mortality from 1975 to 2019, reported Jennifer L. Caswell-Jin, MD, of Stanford University School of Medicine in California, and colleagues in .

Of this reduction, 47% (model range 35%-60%) was associated with treatment of stage I to III breast cancer, while treatment for metastatic breast cancer was associated with 29% (19%-33%), and screening was associated with 25% (21%-33%).

The age-adjusted breast cancer mortality rate in the U.S. was 48 per 100,000 women in 1975 and 27 per 100,000 women in 2019. The models estimated that in the absence of interventions, and with the increase in breast cancer incidence during that time period, the age-adjusted breast cancer mortality rate in 2019 would have been 64 deaths per 100,000 women.

Model-based estimates "highlight the continued need to invest in both early detection and linkage to timely, guideline-concordant treatments for all patients," wrote Ethan Basch, MD, of the University of North Carolina at Chapel Hill, and colleagues in an . "Models such as those developed by CISNET [Cancer Intervention and Surveillance Modeling Network] investigators serve as an essential tool to help clarify and quantify for decision-makers the population health return on decades-long investments in research, clinical care, and public health programming."

Using aggregated observational and clinical trial data on the dissemination and effects of screening and treatment, the four CISNET models simulated U.S. breast cancer mortality rates, including mortality rates by by estrogen receptor (ER) and HER2 status, among women ages 30 to 79 during the study's time period.

The models suggested that breast cancer mortality reduction varied by ER/HER2 status. In 2019, the age-adjusted breast cancer mortality reduction was greatest for ER-positive/HER2-positive disease, at 71% -- from 9.0 per 100,000 women in the absence of intervention to 2.6 per 100,000. The reduction was smallest for ER-negative/HER2-negative disease, at 39% (9.5 to 5.8 per 100,000).

Breast cancer screening was associated with the greatest relative component of the mortality reduction for ER-negative/HER2-negative breast cancer, representing 40%, and with the smallest relative component for ER-positive/HER2-positive breast cancer, representing 19% of the mortality reduction.

In contrast, metastatic treatment was associated with the smallest relative component of the mortality reduction for ER-negative/HER2-negative breast cancer, at 19% of the total mortality reduction, with higher relative components for the other ER/HER2 categories: 30% for ER-positive/HER2-negative disease, 29% for ER-negative/HER2-positive disease, and 29% for ER-positive/HER2-positive disease.

Caswell-Jin and colleagues also noted that the estimated median breast cancer-specific survival after metastatic recurrence changed the most in the simulation models from 2000 to 2019, with the median breast cancer-specific survival improving from a mean of 1.9 years to a mean of 3.2 years.

The greatest improvement was seen in patients with ER-positive/HER2-positive breast cancer (2.5 years), followed by ER-positive/HER2-negative disease (1.6 years) and ER-negative/HER2-positive disease (1.6 years).

The smallest improvement in survival was observed for patients with ER-negative/HER2-negative metastatic recurrent breast cancer (0.5 years).

The editorialists noted that a limitation of this study was that it didn't include evaluations of subpopulation-specific estimates of mortality reductions in marginalized populations.

"Future modeling work should evaluate how changes in screening and treatment affect care and outcome disparities across subpopulations to inform research and implementation planning, as well as interventions and policies to help address gaps and improve equity," they wrote.

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