title: Development and validation of a clinical prediction rule to identify suspected breast cancer: a prospective cohort study.
abstract: BACKGROUND
  The number of primary care referrals of women with breast symptoms to symptomatic breast units (SBUs) has increased exponentially in the past decade in Ireland. The aim of this study is to develop and validate a clinical prediction rule (CPR) to identify women with breast cancer so that a more evidence based approach to referral from primary care to these SBUs can be developed.
  
  
  METHODS
  We analysed routine data from a prospective cohort of consecutive women reviewed at a SBU with breast symptoms. The dataset was split into a derivation and validation cohort. Regression analysis was used to derive a CPR from the patient's history and clinical findings. Validation of the CPR consisted of estimating the number of breast cancers predicted to occur compared with the actual number of observed breast cancers across deciles of risk.
  
  
  RESULTS
  A total of 6,590 patients were included in the derivation study and 4.9% were diagnosed with breast cancer. Independent clinical predictors for breast cancer were: increasing age by year (adjusted odds ratio 1.08, 95% CI 1.07-1.09); presence of a lump (5.63, 95% CI 4.2-7.56); nipple change (2.77, 95% CI 1.68-4.58) and nipple discharge (2.09, 95% CI 1.1-3.97). Validation of the rule (n = 911) demonstrated that the probability of breast cancer was higher with an increasing number of these independent variables. The Hosmer-Lemeshow goodness of fit showed no overall significant difference between the expected and the observed numbers of breast cancer (χ(2)HL: 6.74, p-value: 0.56).
  
  
  CONCLUSIONS
  This study derived and validated a CPR for breast cancer in women attending an Irish national SBU. We found that increasing age, presence of a lump, nipple discharge and nipple change are all associated with increased risk of breast cancer. Further validation of the rule is necessary as well as an assessment of its impact on referral practice.
authors.affiliation: HRB Centre for Primary Care Research, Department of General Practice, Royal College of Surgeons in Ireland, 123 St, Stephen's Green, Dublin 2, Republic of Ireland. rosegalvin@rcsi.ie.
authors.forename: Rose
authors.initials: R
authors.lastname: Galvin
authors.forename: Doireann
authors.initials: D
authors.lastname: Joyce
authors.forename: Eithne
authors.initials: E
authors.lastname: Downey
authors.forename: Fiona
authors.initials: F
authors.lastname: Boland
authors.forename: Tom
authors.initials: T
authors.lastname: Fahey
authors.forename: Arnold K
authors.initials: AK
authors.lastname: Hill
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology; D055088:Early Detection of Cancer / Q000379:methods*; D019317:Evidence-Based Medicine; D005260:Female; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D008875:Middle Aged; D011446:Prospective Studies; D012044:Regression Analysis; D018570:Risk Assessment; D012307:Risk Factors; D055815:Young Adult