title: Breast Cancer Screening, Incidence, and Mortality Across US Counties.
abstract: OBJECTIVE
  Screening mammography rates vary considerably by location in the United States, providing a natural opportunity to investigate the associations of screening with breast cancer incidence and mortality, which are subjects of debate.
  
  
  OBJECTIVE
  To examine the associations between rates of modern screening mammography and the incidence of breast cancer, mortality from breast cancer, and tumor size.
  
  
  METHODS
  An ecological study of 16 million women 40 years or older who resided in 547 counties reporting to the Surveillance, Epidemiology, and End Results cancer registries during the year 2000. Of these women, 53,207 were diagnosed with breast cancer that year and followed up for the next 10 years. The study covered the period January 1, 2000, to December 31, 2010, and the analysis was performed between April 2013 and March 2015.
  
  
  METHODS
  Extent of screening in each county, assessed as the percentage of included women who received a screening mammogram in the prior 2 years.
  
  
  METHODS
  Breast cancer incidence in 2000 and incidence-based breast cancer mortality during the 10-year follow-up. Incidence and mortality were calculated for each county and age adjusted to the US population.
  
  
  RESULTS
  Across US counties, there was a positive correlation between the extent of screening and breast cancer incidence (weighted r = 0.54; P < .001) but not with breast cancer mortality (weighted r = 0.00; P = .98). An absolute increase of 10 percentage points in the extent of screening was accompanied by 16% more breast cancer diagnoses (relative rate [RR], 1.16; 95% CI, 1.13-1.19) but no significant change in breast cancer deaths (RR, 1.01; 95% CI, 0.96-1.06). In an analysis stratified by tumor size, we found that more screening was strongly associated with an increased incidence of small breast cancers (≤2 cm) but not with a decreased incidence of larger breast cancers (>2 cm). An increase of 10 percentage points in screening was associated with a 25% increase in the incidence of small breast cancers (RR, 1.25; 95% CI, 1.18-1.32) and a 7% increase in the incidence of larger breast cancers (RR, 1.07; 95% CI, 1.02-1.12).
  
  
  CONCLUSIONS
  When analyzed at the county level, the clearest result of mammography screening is the diagnosis of additional small cancers. Furthermore, there is no concomitant decline in the detection of larger cancers, which might explain the absence of any significant difference in the overall rate of death from the disease. Together, these findings suggest widespread overdiagnosis.
authors.affiliation: Currently in private practice, Seattle, Washington.
authors.forename: Charles
authors.initials: C
authors.lastname: Harding
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pompei
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts.
authors.forename: Dmitriy
authors.initials: D
authors.lastname: Burmistrov
authors.affiliation: Department of Medicine, The Dartmouth Institute for Health Policy and Clinical Practice, Hanover, New Hampshire.
authors.forename: H Gilbert
authors.initials: HG
authors.lastname: Welch
authors.affiliation: Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts.
authors.forename: Rediet
authors.initials: R
authors.lastname: Abebe
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts.
authors.forename: Richard
authors.initials: R
authors.lastname: Wilson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality* / Q000473:pathology; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000706:statistics & numerical data*; D000069342:Medical Overuse; D008875:Middle Aged; D014481:United States / Q000453:epidemiology