title: Basal-like phenotype is not associated with patient survival in estrogen-receptor-negative breast cancers.
abstract: BACKGROUND
  Basal-phenotype or basal-like breast cancers are characterized by basal epithelium cytokeratin (CK5/14/17) expression, negative estrogen receptor (ER) status and distinct gene expression signature. We studied the clinical and biological features of the basal-phenotype tumors determined by immunohistochemistry (IHC) and cDNA microarrays especially within the ER-negative subgroup.
  
  
  METHODS
  IHC was used to evaluate the CK5/14 status of 445 stage II breast cancers. The gene expression signature of the CK5/14 immunopositive tumors was investigated within a subset (100) of the breast tumors (including 50 ER-negative tumors) with a cDNA microarray. Survival for basal-phenotype tumors as determined by CK5/14 IHC and gene expression signature was assessed.
  
  
  RESULTS
  From the 375 analyzable tumor specimens, 48 (13%) were immunohistochemically positive for CK5/14. We found adverse distant disease-free survival for the CK5/14-positive tumors during the first years (3 years hazard ratio (HR) 2.23, 95% confidence interval (CI) 1.17 to 4.24, p = 0.01; 5 years HR 1.80, 95% CI 1.02 to 3.15, p = 0.04) but the significance was lost at the end of the follow-up period (10 years HR 1.43, 95% CI 0.84 to 2.43, p = 0.19). Gene expression profiles of immunohistochemically determined CK5/14-positive tumors within the ER-negative tumor group implicated 1,713 differently expressed genes (p < 0.05). Hierarchical clustering analysis with the top 500 of these genes formed one basal-like and a non-basal-like cluster also within the ER-negative tumor entity. A highly concordant classification could be constructed with a published gene set (Sorlie's intrinsic gene set, concordance 90%). Both gene sets identified a basal-like cluster that included most of the CK5/14-positive tumors, but also immunohistochemically CK5/14-negative tumors. Within the ER-negative tumor entity there was no survival difference between the non-basal and basal-like tumors as identified by immunohistochemical or gene-expression-based classification.
  
  
  CONCLUSIONS
  Basal cytokeratin-positive tumors have a biologically distinct gene expression signature from other ER-negative tumors. Even if basal cytokeratin expression predicts early relapse among non-selected tumors, the clinical outcome of basal tumors is similar to non-basal ER-negative tumors. Immunohistochemically basal cytokeratin-positive tumors almost always belong to the basal-like gene expression profile, but this cluster also includes few basal cytokeratin-negative tumors.
authors.affiliation: Department of Pathology, Seinäjoki Central Hospital, Hanneksenrinne 7, FIN-60220 Seinäjoki, Finland. mervi.jumppanen@epshp.fi
authors.forename: Mervi
authors.initials: M
authors.lastname: Jumppanen
authors.forename: Sofia
authors.initials: S
authors.lastname: Gruvberger-Saal
authors.forename: Päivikki
authors.initials: P
authors.lastname: Kauraniemi
authors.forename: Minna
authors.initials: M
authors.lastname: Tanner
authors.forename: Pär-Ola
authors.initials: PO
authors.lastname: Bendahl
authors.forename: Mikael
authors.initials: M
authors.lastname: Lundin
authors.forename: Morten
authors.initials: M
authors.lastname: Krogh
authors.forename: Pasi
authors.initials: P
authors.lastname: Kataja
authors.forename: Ake
authors.initials: A
authors.lastname: Borg
authors.forename: Mårten
authors.initials: M
authors.lastname: Fernö
authors.forename: Jorma
authors.initials: J
authors.lastname: Isola
mesh_terms: D001943:Breast Neoplasms / Q000473:pathology*; D015331:Cohort Studies; D018572:Disease-Free Survival; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D007150:Immunohistochemistry; D053547:Keratin-14 / Q000378:metabolism; D053555:Keratin-5 / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D011960:Receptors, Estrogen; D016019:Survival Analysis
chemical_list: D053547:Keratin-14; D053555:Keratin-5; D011960:Receptors, Estrogen