title: Breast cancer risk factors according to joint estrogen receptor and progesterone receptor status.
abstract: BACKGROUND
  We investigated risk factor patterns for subtypes of breast cancer characterized by joint estrogen receptor (ER) and progesterone receptor (PR) status in a hospital-based case-control study.
  
  
  METHODS
  ER and PR tumor status were determined immunohisotchemically. Risk factors of interest were entered into a multiple polychotomous logistic regression model simultaneously; odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Using this model, cases in the four tumor subtypes (ER+PR+, ER-PR-, ER+PR-, ER-PR+) were compared simultaneously to controls. A Wald test for heterogeneity across the four subtypes was conducted, as well as a case-case comparison between the two most biologically disparate subtypes, ER+PR+ and ER-PR-.
  
  
  RESULTS
  The receptor status distribution was as follows: 33% ER+PR+, 34% ER-PR-, 20% ER+PR-, and 13% ER-PR+. Among 317 cases and 401 controls, we found significant heterogeneity across the four tumor subtypes for older age at first full-term pregnancy (p=0.04) and post-menopausal status (p=0.04). For older age at first full-term pregnancy, an elevated risk was found for the ER+PR- subtype (OR=2.5; 95% CI: 1.2-5.1). For post-menopausal status, elevated risks were found for both the ER+PR+ (OR=2.4; 95% CI: 1.1-4.9) and ER+PR- (OR=7.2; 95% CI: 2.4-21.7) subtypes. From the case-case comparisons, we found that cases, who had consumed alcohol for more than 1 year were 3.4 times more likely to have ER+PR+ tumors than ER-PR- tumors (95% CI: 1.4-8.4).
  
  
  CONCLUSIONS
  Certain breast cancer risk factors may vary by ER and PR status, and joint ER/PR status should be taken into account in future studies of risk factor estimates.
authors.affiliation: Department of Epidemiology and Public Health, Yale University, School of Medicine, New Haven, CT, USA. rusieckj@mail.nih.gov
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Rusiecki
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Holford
authors.forename: Shelia H
authors.initials: SH
authors.lastname: Zahm
authors.forename: Tongzhang
authors.initials: T
authors.lastname: Zheng
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000209:etiology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008593:Menopause; D008875:Middle Aged; D008962:Models, Theoretical; D016017:Odds Ratio; D010298:Parity; D011247:Pregnancy; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D018570:Risk Assessment
chemical_list: D011960:Receptors, Estrogen; D011980:Receptors, Progesterone