title: Intratumor heterogeneity and precision of microarray-based predictors of breast cancer biology and clinical outcome.
abstract: OBJECTIVE
  Identifying sources of variation in expression microarray data and the effect of variance in gene expression measurements on complex predictive and diagnostic models is essential when translating microarray-based experimental approaches into clinical assays. The technical reproducibility of microarray platforms is well established. Here, we investigate the additional impact of intratumor heterogeneity, a largely unstudied component of variance, on the performance of several microarray-based assays in breast cancer.
  
  
  METHODS
  Genome-wide expression profiling was performed on 50 core needle biopsies from 18 breast cancer patients using Affymetrix GeneChip Human Genome U133 Plus 2.0 arrays. Global profiles of expression were characterized using unsupervised clustering methods and variance components models. Array-based measures of estrogen receptor (ER) and progesterone receptor (PR) status were compared with immunohistochemistry. The precision of genomic predictors of ER pathway status, recurrence risk, and sensitivity to chemotherapeutics was evaluated by interclass correlation.
  
  
  RESULTS
  Global patterns of gene expression demonstrated that intratumor variation was substantially less than the total variation observed across the patient population. Nevertheless, a fraction of genes exhibited significant intratumor heterogeneity in expression. A high degree of reproducibility was observed in single-gene predictors of ER (intraclass correlation coefficient [ICC] = 0.94) and PR expression (ICC = 0.90), and in a multigene predictor of ER pathway activation (ICC = 0.98) with high concordance with immunohistochemistry. Substantial agreement was also observed for multigene signatures of cancer recurrence (ICC = 0.71) and chemotherapeutic sensitivity (ICC = 0.72 and 0.64).
  
  
  CONCLUSIONS
  Intratumor heterogeneity, although present at the level of individual gene expression, does not preclude precise microarray-based predictions of tumor behavior or clinical outcome in breast cancer patients.
authors.affiliation: Department of Biostatistics, Duke University Medical Center, Medical Center Box 3712, Durham, NC 27710, USA.
authors.forename: William T
authors.initials: WT
authors.lastname: Barry
authors.forename: Dawn N
authors.initials: DN
authors.lastname: Kernagis
authors.forename: Holly K
authors.initials: HK
authors.lastname: Dressman
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Griffis
authors.forename: J'vonne D
authors.initials: JD
authors.lastname: Hunter
authors.forename: John A
authors.initials: JA
authors.lastname: Olson
authors.forename: Jeff R
authors.initials: JR
authors.lastname: Marks
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Ginsburg
authors.forename: Paul K
authors.initials: PK
authors.lastname: Marcom
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Nevins
authors.forename: Joseph
authors.initials: J
authors.lastname: Geradts
authors.forename: Michael B
authors.initials: MB
authors.lastname: Datto
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D001707:Biopsy, Needle; D001943:Breast Neoplasms / Q000737:chemistry / Q000188:drug therapy / Q000235:genetics* / Q000401:mortality / Q000473:pathology*; D016000:Cluster Analysis; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods*; D015972:Gene Expression Regulation, Neoplastic; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D009367:Neoplasm Staging; D020411:Oligonucleotide Array Sequence Analysis; D011237:Predictive Value of Tests; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis; D012008:Recurrence; D015203:Reproducibility of Results; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C508053:ERBB2 protein, human