BRCA1 dysfunction in sporadic basal-like breast cancer

Oncogene. 2007 Mar 29;26(14):2126-32. doi: 10.1038/sj.onc.1210014. Epub 2006 Oct 2.


Basal-like breast cancers form a distinct subtype of breast cancer characterized by the expression of markers expressed in normal basal/myoepithelial cells. Breast cancers arising in carriers of germline BRCA1 mutations are predominately of basal-like type, suggesting that BRCA1 dysfunction may play a role in the pathogenesis of sporadic basal-like cancers. We analysed 37 sporadic breast cancers expressing the basal marker cytokeratin 5/6, and age- and grade-matched controls, for downregulation of BRCA1. Although BRCA1 promoter methylation was no more common in basal-like cancers (basal 14% vs controls 11%, P=0.72), BRCA1 messenger RNA expression was twofold lower in basal-like breast cancers compared to matched controls (P=0.008). ID4, a negative regulator of BRCA1, was expressed at 9.1-fold higher levels in basal-like breast cancer (P<0.0001), suggesting a potential mechanism of BRCA1 downregulation. BRCA1 downregulation correlated with the presence of multiple basal markers, revealing heterogeneity in the basal-like phenotype. Finally, we found that 63% of metaplastic breast cancers, a rare type of basal-like cancers, had BRCA1 methylation, in comparison to 12% of controls (P<0.0001). The high prevalence of BRCA1 dysfunction identified in this study could be exploited in the development of novel approaches to targeted treatment of basal-like breast cancer.

MeSH terms

  • BRCA1 Protein / genetics*
  • Breast Neoplasms / genetics*
  • Breast Neoplasms / pathology*
  • DNA Methylation
  • Down-Regulation
  • Female
  • Gene Expression Regulation, Neoplastic*
  • Humans
  • Keratin-5 / analysis
  • Keratin-6 / analysis
  • Promoter Regions, Genetic
  • RNA, Messenger / analysis
  • RNA, Messenger / metabolism


  • BRCA1 Protein
  • Keratin-5
  • Keratin-6
  • RNA, Messenger