title: Survival analysis of contralateral prophylactic mastectomy: a question of selection bias.
abstract: BACKGROUND
  Rates of contralateral prophylactic mastectomy (CPM) in women with breast cancer have increased, but most studies fail to show a survival benefit. We evaluated survival among CPM patients compared to patients undergoing single mastectomy (SM).
  
  
  METHODS
  The Surveillance, Epidemiology, and End Results database was used to identify unilateral breast cancer patients who underwent mastectomy with/without CPM from 1998 to 2010. Case-control analysis was performed with CPM cases matched to SM controls on the basis of age group, race/ethnicity, extent of surgery, grade, T classification, N classification, estrogen receptor status, and propensity score. Survival analyses included Kaplan-Meier curves and univariate and multivariate proportional hazard models to determine factors associated with disease-specific (DSS) and overall survival (OS).
  
  
  RESULTS
  A total of 26,526 CPM patients were identified. On multivariate regression analysis, increasing age, greater extent of surgery, increasing T and N stage, African American race, Hispanic ethnicity, poorly differentiated grade, and estrogen receptor negativity were associated with increased risk of death. CPM was associated with improved DSS (HR 0.86, 95 % CI 0.79-0.93) and even greater OS (HR 0.76, 95 % CI 0.71-0.81) compared with SM. Contralateral breast cancer (CBC) occurred in 1.6 % of women in the cohort. Removing CBC cases from analysis had little impact on CPM DSS (HR 0.86, 95 % CI 0.79-0.93) and OS (0.77, 95 % CI 0.72-0.82) suggesting that prevention of CBC by CPM does not explain the observed survival benefit.
  
  
  CONCLUSIONS
  CPM rates continue to rise. The improved DSS and OS observed with CPM support selection bias. Prospective trials are needed to determine cohorts of patients most likely to benefit from CPM.
authors.affiliation: Department of Surgical Oncology, City of Hope National Medical Center, Duarte, CA, USA, lkruper@coh.org.
authors.forename: Laura
authors.initials: L
authors.lastname: Kruper
authors.forename: Rondi M
authors.initials: RM
authors.lastname: Kauffmann
authors.forename: David D
authors.initials: DD
authors.lastname: Smith
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Nelson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000453:epidemiology / Q000401:mortality* / Q000601:surgery*; D002140:California / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008207:Lymphatic Metastasis; D008408:Mastectomy / Q000401:mortality*; D008875:Middle Aged; D015999:Multivariate Analysis; D060787:Neoplasm Grading; D009367:Neoplasm Staging; D011379:Prognosis; D018426:SEER Program; D015983:Selection Bias; D015996:Survival Rate; D055815:Young Adult