Research article

Basal-like phenotype is not associated with patient survival in estrogen-receptor-negative breast cancers

Mervi Jumppanen^1,2* , Sofia Gruvberger-Saal^3* , Päivikki Kauraniemi² , Minna Tanner^2,4 , Pär-Ola Bendahl³ , Mikael Lundin⁵ , Morten Krogh⁶ , Pasi Kataja² , Åke Borg³ , Mårten Fernö³ and Jorma Isola²

¹  Department of Pathology, Seinäjoki Central Hospital, Hanneksenrinne 7, FIN-60220 Seinäjoki, Finland

²  Institute of Medical Technology, University and University Hospital of Tampere, Biokatu 6, FIN-33520 Tampere, Finland

³  Department of Oncology, Clinical Sciences, University of Lund, Klinikgatan 7, SE-221 85 Lund, Sweden

⁴  Department of Oncology, Tampere University Hospital, Teiskontie 35, FIN-33520 Tampere, Finland

⁵  Biomedical Informatics group, Department of Oncology, University of Helsinki, Haartmanninkatu 8, FIN-00290 Helsinki, Finland

⁶  Department of Theoretical Physics, Lund University, Sölvegatan 14A, SE-221 85 Lund, Sweden

author email corresponding author email* Contributed equally

Breast Cancer Research 2007, 9:R16doi:10.1186/bcr1649

Published:	31 January 2007

Abstract

Introduction

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.

Conclusion

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.