title: Prognosis of early-stage synchronous bilateral invasive breast cancer.
abstract: BACKGROUND
  Contradictory data exists concerning the prognosis of patients with synchronous bilateral breast cancer (SBBC). Most authors report a worse prognosis for SBBC patients compared to unilateral breast cancer (UBC) patients. There are a few studies that did not support these findings. This study gives a comprehensive picture of SBBC and tests the hypothesis that outcome of this entity is based on the tumor with the worse prognosis (reference lesion).
  
  
  METHODS
  The data of two prospective Swiss breast cancer databases covering a 20-year period (1990-2009) was reviewed. Forty-six cases of SBBC were identified. In 34 patients with early-stage SBBC, the reference lesions (defined as the tumor with the more advanced stage or, in cases where both tumors had the same stage, the larger tumor) were compared in a case-control approach with 100 patients having UBC (SBBC/UBC ratio = 1/3). The controls were matched for age, time of diagnosis, tumor size, axillary node status, histological grade and estrogen-receptor status. Differences in terms of survival curves were analyzed using the log rank test; the possible correlation between matched groups was evaluated by a frailty Cox model.
  
  
  RESULTS
  There were no significant differences in disease-specific survival between SBBC and its unilateral controls (HR, 0.932; 95% CI, 0.322-1.07; p = 0.90).
  
  
  CONCLUSIONS
  The prognosis of SBBC was determined by the reference lesion; the contralateral second tumor had no additional impact on outcome.
authors.affiliation: Department of Gynecology and Obstetrics, University Hospital Basel, Spitalstrasse 21, CH-4031 Basel, Switzerland.
authors.forename: S M
authors.initials: SM
authors.lastname: Schmid
authors.forename: C
authors.initials: C
authors.lastname: Pfefferkorn
authors.forename: M E
authors.initials: ME
authors.lastname: Myrick
authors.forename: C T
authors.initials: CT
authors.lastname: Viehl
authors.forename: E
authors.initials: E
authors.lastname: Obermann
authors.forename: A
authors.initials: A
authors.lastname: Schötzau
authors.forename: U
authors.initials: U
authors.lastname: Güth
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000401:mortality* / Q000473:pathology / Q000601:surgery; D018270:Carcinoma, Ductal, Breast / Q000401:mortality* / Q000473:pathology / Q000601:surgery; D018275:Carcinoma, Lobular / Q000401:mortality* / Q000473:pathology / Q000601:surgery; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008875:Middle Aged; D009367:Neoplasm Staging; D009378:Neoplasms, Multiple Primary / Q000401:mortality* / Q000473:pathology / Q000601:surgery; D011379:Prognosis; D016016:Proportional Hazards Models; D015996:Survival Rate