title: Haptoglobin phenotype is not a predictor of recurrence free survival in high-risk primary breast cancer patients.
abstract: BACKGROUND
  Better breast cancer prognostication may improve selection of patients for adjuvant therapy. We conducted a retrospective follow-up study in which we investigated sera of high-risk primary breast cancer patients, to search for proteins predictive of recurrence free survival.
  
  
  METHODS
  Two sample sets of high-risk primary breast cancer patients participating in a randomised national trial investigating the effectiveness of high-dose chemotherapy were analysed. Sera in set I (n = 63) were analysed by surface enhanced laser desorption ionisation time-of-flight mass spectrometry (SELDI-TOF MS) for biomarker finding. Initial results were validated by analysis of sample set II (n = 371), using one-dimensional gel-electrophoresis.
  
  
  RESULTS
  In sample set I, the expression of a peak at mass-to-charge ratio 9198 (relative intensity <or= 20 or > 20), identified as haptoglobin (Hp) alpha-1 chain, was strongly associated with recurrence free survival (global Log-rank test; p = 0.0014). Haptoglobin is present in three distinct phenotypes (Hp 1-1, Hp 2-1, and Hp 2-2), of which only individuals with phenotype Hp 1-1 or Hp 2-1 express the haptoglobin alpha-1 chain. As the expression of the haptoglobin alpha-1 chain, determined by SELDI-TOF MS, corresponds to the phenotype, initial results were validated by haptoglobin phenotyping of the independent sample set II by native one-dimensional gel-electrophoresis. With the Hp 1-1 phenotype as the reference category, the univariate hazard ratio for recurrence was 0.87 (95% CI: 0.56 - 1.34, p = 0.5221) and 1.03 (95% CI: 0.65 - 1.64, p = 0.8966) for the Hp 2-1 and Hp 2-2 phenotypes, respectively, in sample set II.
  
  
  CONCLUSIONS
  In contrast to our initial results, the haptoglobin phenotype was not identified as a predictor of recurrence free survival in high-risk primary breast cancer in our validation set. Our initial observation in the discovery set was probably the result of a type I error (i.e. false positive). This study illustrates the importance of validation in obtaining the true clinical applicability of a potential biomarker.
authors.affiliation: Department of Pharmacy & Pharmacology, Netherlands Cancer Institute/Slotervaart Hospital, Amsterdam, the Netherlands. marie-christine.gast@slz.nl
authors.forename: Marie-Christine W
authors.initials: MC
authors.lastname: Gast
authors.forename: Harm
authors.initials: H
authors.lastname: van Tinteren
authors.forename: Marijke
authors.initials: M
authors.lastname: Bontenbal
authors.forename: René Q G C M
authors.initials: RQ
authors.lastname: van Hoesel
authors.forename: Marianne A
authors.initials: MA
authors.lastname: Nooij
authors.forename: Sjoerd
authors.initials: S
authors.lastname: Rodenhuis
authors.forename: Paul N
authors.initials: PN
authors.lastname: Span
authors.forename: Vivianne C G
authors.initials: VC
authors.lastname: Tjan-Heijnen
authors.forename: Elisabeth G E
authors.initials: EG
authors.lastname: de Vries
authors.forename: Nathan
authors.initials: N
authors.lastname: Harris
authors.forename: Jos W R
authors.initials: JW
authors.lastname: Twisk
authors.forename: Jan H M
authors.initials: JH
authors.lastname: Schellens
authors.forename: Jos H
authors.initials: JH
authors.lastname: Beijnen
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000401:mortality / Q000473:pathology; D018572:Disease-Free Survival; D004586:Electrophoresis; D005260:Female; D006242:Haptoglobins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D053208:Kaplan-Meier Estimate; D008207:Lymphatic Metastasis; D013058:Mass Spectrometry; D008408:Mastectomy; D008875:Middle Aged; D009367:Neoplasm Staging; D010641:Phenotype; D012008:Recurrence
chemical_list: C485359:HP protein, human; D006242:Haptoglobins