title: A population-based study of bilateral prophylactic mastectomy efficacy in women at elevated risk for breast cancer in community practices.
abstract: BACKGROUND
  Findings from several studies suggest that bilateral prophylactic mastectomy reduces breast cancer incidence by 90% or more, but the studies used highly selected patients from referral centers, and the comparison groups were not population based. We studied the efficacy of bilateral prophylactic mastectomy in women with elevated breast cancer risk cared for in community practices.
  
  
  METHODS
  We conducted a retrospective case-cohort study of women aged 18 to 80 years with 1 or more breast cancer risk factors (family history of breast cancer, history of atypical hyperplasia, or > or =1 breast biopsies with benign findings). Using computerized data and medical records, we identified 276 women with bilateral prophylactic mastectomy and a stratified random sample of 196 women representing an underlying cohort of 666 800 women with elevated breast cancer risk without prophylactic mastectomy, and then we determined who developed breast cancer.
  
  
  RESULTS
  Breast cancer developed in 1 woman (0.4%) after bilateral prophylactic mastectomy vs 26 800 women (4.0%) without prophylactic mastectomy. Stratifying by birth year, the hazard ratio for breast cancer occurrence after bilateral prophylactic mastectomy was 0.005 (95% confidence interval, 0.001-0.044). No woman with bilateral prophylactic mastectomy died of breast cancer vs a calculated 0.2% of women without prophylactic mastectomy.
  
  
  CONCLUSIONS
  Bilateral prophylactic mastectomy reduced breast cancer incidence in women at elevated risk for breast cancer cared for in community-based practices. However, the absolute risk of breast cancer incidence and death in women who did not undergo the procedure in these settings was relatively low.
authors.affiliation: Research and Evaluation Department, Southern California Permanente Medical Group, 100 S. Los Robles, Pasadena, CA 91101, USA. ann.m.geiger@kp.org
authors.forename: Ann M
authors.initials: AM
authors.lastname: Geiger
authors.forename: Onchee
authors.initials: O
authors.lastname: Yu
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Herrinton
authors.forename: William E
authors.initials: WE
authors.lastname: Barlow
authors.forename: Emily L
authors.initials: EL
authors.lastname: Harris
authors.forename: Sharon
authors.initials: S
authors.lastname: Rolnick
authors.forename: Mary B
authors.initials: MB
authors.lastname: Barton
authors.forename: Joann G
authors.initials: JG
authors.lastname: Elmore
authors.forename: Suzanne W
authors.initials: SW
authors.lastname: Fletcher
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*; D005260:Female; D006801:Humans; D015994:Incidence; D015413:Mastectomy, Simple / Q000379:methods*; D008875:Middle Aged; D011322:Primary Prevention / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D016896:Treatment Outcome