Air Pollution, Clustering of Particulate Matter Components, and Breast Cancer in the Sister Study: A U.S.-Wide Cohort

Environ Health Perspect. 2019 Oct;127(10):107002. doi: 10.1289/EHP5131. Epub 2019 Oct 9.


Background: Particulate matter (PM) is a complex mixture. Geographic variations in PM may explain the lack of consistent associations with breast cancer.

Objective: We aimed to evaluate the relationship between air pollution, PM components, and breast cancer risk in a United States-wide prospective cohort.

Methods: We estimated annual average ambient residential levels of particulate matter <2.5 μm and <10 μm in aerodynamic diameter (PM2.5 and PM10, respectively) and nitrogen dioxide (NO2) using land-use regression for 47,433 Sister Study participants (breast cancer-free women with a sister with breast cancer) living in the contiguous United States. Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for risk associated with an interquartile range (IQR) increase in pollutants. Predictive k-means were used to assign participants to clusters derived from PM2.5 component profiles to evaluate the impact of heterogeneity in the PM2.5 mixture. For PM2.5, we investigated effect measure modification by component cluster membership and by geographic region without regard to air pollution mixture.

Results: During follow-up (mean=8.4 y), 2,225 invasive and 623 ductal carcinoma in situ (DCIS) cases were identified. PM2.5 and NO2 were associated with breast cancer overall [HR=1.05 (95% CI:0.99, 1.11) and 1.06 (95% CI:1.02, 1.11), respectively] and with DCIS but not with invasive cancer. Invasive breast cancer was associated with PM2.5 only in the Western United States [HR=1.14 (95% CI:1.02, 1.27)] and NO2 only in the Southern United States [HR=1.16 (95% CI:1.01, 1.33)]. PM2.5 was associated with a higher risk of invasive breast cancer among two of seven identified composition-based clusters. A higher risk was observed [HR=1.25 (95% CI: 0.97, 1.60)] in a California-based cluster characterized by low S and high Na and nitrate (NO3-) fractions and for another Western United States cluster [HR=1.60 (95% CI: 0.90, 2.85)], characterized by high fractions of Si, Ca, K, and Al.

Conclusion: Air pollution measures were related to both invasive breast cancer and DCIS within certain geographic regions and PM component clusters.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Adult
  • Air Pollutants*
  • Air Pollution / statistics & numerical data*
  • Breast Neoplasms / epidemiology*
  • Environmental Exposure / statistics & numerical data*
  • Female
  • Humans
  • Middle Aged
  • Particulate Matter*
  • United States / epidemiology


  • Air Pollutants
  • Particulate Matter