BACKGROUND AND PURPOSE:

• Breast cancer mortality has declined in the US since 1975
  • It’s not clear whether this decline is due to improved treatment of metastatic breast cancer or some other factor
• Caswell-Jin et al. (JAMA, 2024), estimated the impact of various factors, including newer breast cancer treatments, on the reduction in breast cancer mortality

METHODS:

• Cancer Intervention and Surveillance Modeling Network (CISNET) models
  • Based on aggregated observational and clinical trial data
  • From 1975 to 2019
• Simulated population
  • Women aged 30 to 79
• Exposures
  • Screening mammography | Treatment of stage I to III breast cancer | Treatment of metastatic breast cancer
• Study design
  • The authors simulated death due to breast cancer, overall and by estrogen receptor and ERBB2 (formerly HER2) status
• Primary outcome
  • Model-estimated age-adjusted breast cancer mortality rate associated with exposures
  • Model-estimated median survival after breast cancer metastatic recurrence

RESULTS:

• Age-adjusted breast cancer mortality rate in the US
  • 1975: 48 per 100,000 women
  • 2019: 27 per 100,000 women
• Reduction in breast cancer mortality in 2019: 58% (model range, 55 to 61)
  • Reduction associated with treatment of metastatic breast cancer: 29% (range 19 to 33)
  • Reduction associated with treatment of stage I to III breast cancer: 47% (range, 35 to 60)
  • Reduction associated with mammography screening: 25% (range, 21 to 33)
• The greatest change in survival after metastatic recurrence occurred between 2000 and 2019
  • 2000: 1.9 years (range, 1.0 to 2.7)
  • 2019: 3.2 years (range, 2.0 to 4.9)
• Median survival for estrogen receptor (ER)–positive/ERBB2-positive breast cancer improved by 2.5 years (range, 2.0 to 3.4)
• Median survival for ER−/ERBB2− breast cancer improved by 0.5 years (range, 0.3 to 0.8)

CONCLUSION:

• By 2019, model simulations suggest that breast cancer mortality is down 58% from 1975 mortality rates in association with newer treatments and screening guidelines
  • Treatment for stage I to III breast cancer was associated with 47% of this reduction
  • Treatment of metastatic cancer accounted for 29% of this reduction, and mammography screening for 25%
• The authors state

Breast cancer screening accounts for an increasingly smaller proportion of breast cancer mortality reduction as improvements in stage I to III therapy continue

However, the absolute contribution of screening to mortality reduction remained consistent in the models, emphasizing that cancers diagnosed in the absence of screening were associated with poorer outcomes that cannot be overcome with modern treatments

Learn More – Primary Sources:

Analysis of Breast Cancer Mortality in the US—1975 to 2019