title: The Effect of California's Breast Density Notification Legislation on Breast Cancer Screening.
abstract: OBJECTIVE
  Half of US states mandate women be notified if they have dense breasts on their mammogram, yet guidelines and data on supplemental screening modalities are limited. Breast density (BD) refers to the extent that breast tissue appears radiographically dense on mammograms. High BD reduces the sensitivity of screening mammography and increases breast cancer risk. The aim of this study was to determine the potential impact of California's 2013 BD notification legislation on breast cancer screening patterns.
  
  
  METHODS
  We conducted a cohort study of women aged 40 to 74 years who were members of a large Northern California integrated health plan (approximately 3.9 million members) in 2011-2015. We calculated pre- and post-legislation rates of screening mammography and magnetic resonance imaging (MRI). We also examined whether women with dense breasts (defined as BI-RADS density c or d) had higher MRI rates than women with nondense breasts (defined as BI-RADS density a or b).
  
  
  RESULTS
  After adjustment for race/ethnicity, age, body mass index, medical facility, neighborhood median income, and cancer history, there was a relative 6.6% decrease (relative risk [RR] 0.934, confidence interval [CI] 0.92-0.95) in the rate of screening mammography, largely driven by a decrease among women <50 years. While infrequent, there was a relative 16% increase (RR 1.16, CI 1.07-1.25) in the rate of screening MRI, with the greatest increase among the youngest women. In the postlegislation period, women with extremely dense breasts (BI-RADS d) had 2.77 times (CI 1.93-3.95) the odds of a MRI within 9 months of a screening mammogram compared with women with nondense breasts (BI-RADS b).
  
  
  CONCLUSIONS
  In this setting, MRI rates increased in the postlegislation period. In addition, women with higher BD were more likely to have supplementary MRI. The decrease in mammography rates seen primarily among younger women may have been due to changes in national screening guidelines.
authors: 1 Kaiser Permanente Oakland Medical Center, Oakland, CA, USA.
authors: Stephanie Lynn
authors: SL
authors: Chau
authors: 2 Kaiser Permanente Northern California, Oakland, CA, USA.
authors: Amy
authors: A
authors: Alabaster
authors: 2 Kaiser Permanente Northern California, Oakland, CA, USA.
authors: Karin
authors: K
authors: Luikart
authors: 2 Kaiser Permanente Northern California, Oakland, CA, USA.
authors: Leslie Manace
authors: LM
authors: Brenman
authors: 2 Kaiser Permanente Northern California, Oakland, CA, USA.
authors: Laurel A
authors: LA
authors: Habel
mesh_terms: D000328:Adult; D000368:Aged; D001940:Breast / Q000000981:diagnostic imaging; D000071060:Breast Density; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging; D002140:California; D015331:Cohort Studies; D030881:Disclosure / Q000331:legislation & jurisprudence*; D055088:Early Detection of Cancer; D005260:Female; D006801:Humans; D007883:Legislation, Medical; D008279:Magnetic Resonance Imaging; D008327:Mammography; D008403:Mass Screening / Q000331:legislation & jurisprudence* / Q000379:methods; D008875:Middle Aged; D012306:Risk
keywords: California; breast MRI; breast cancer; breast density; cancer screening; mammography; notification legislation; supplementary screening