title: BRCA1 dysfunction in sporadic basal-like breast cancer.
abstract: 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.
authors.affiliation: Chester Beatty Laboratories, The Breakthrough Breast Cancer Research Centre, Institute of Cancer Research, London, UK.
authors.forename: N C
authors.initials: NC
authors.lastname: Turner
authors.forename: J S
authors.initials: JS
authors.lastname: Reis-Filho
authors.forename: A M
authors.initials: AM
authors.lastname: Russell
authors.forename: R J
authors.initials: RJ
authors.lastname: Springall
authors.forename: K
authors.initials: K
authors.lastname: Ryder
authors.forename: D
authors.initials: D
authors.lastname: Steele
authors.forename: K
authors.initials: K
authors.lastname: Savage
authors.forename: C E
authors.initials: CE
authors.lastname: Gillett
authors.forename: F C
authors.initials: FC
authors.lastname: Schmitt
authors.forename: A
authors.initials: A
authors.lastname: Ashworth
authors.forename: A N
authors.initials: AN
authors.lastname: Tutt
mesh_terms: D019313:BRCA1 Protein / Q000235:genetics*; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology*; D019175:DNA Methylation; D015536:Down-Regulation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053555:Keratin-5 / Q000032:analysis; D053553:Keratin-6 / Q000032:analysis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism
chemical_list: D019313:BRCA1 Protein; D053555:Keratin-5; D053553:Keratin-6; D012333:RNA, Messenger