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Molecular Characterization of Basal-like and Non-Basal-like Triple-Negative Breast Cancers

ABSTRACT: Triple-negative (TN) and Basal-like (BL) breast cancer definitions have been used interchangeably to identify breast cancers that lack expression of the hormonal receptors (HR) and overexpression and/or amplification of HER2. However, both classifications when compared to each other, show substantial discordance rates. Here, we molecularly characterize TN tumors, and Basal-like tumors, and compare and contrast the results in terms of common patterns and distinct patterns for each. In total, when testing 412 TN and 473 Basal-like tumors, 21.4% and 31.5% were identified as non-Basal-like and non-TN, respectively. TN tumors identified as Luminal or HER2-enriched showed undistinguishable overall gene expression profiles when compared versus Luminal or HER2-enriched tumors that were not TN. Similar findings were observed within Basal-like tumors regardless of the TN status. Interestingly, most TN tumors identified as HER2-enriched showed low HER2 expression and lack of HER2 amplification despite the similar overall gene expression profiles to HER2-E tumors that were not TN. Lastly, additional genomic classifications are examined within TN and Basal-like cancers, most of which are largely concordant with tumor intrinsic subtype. These results suggest that future clinical trials focused on TN disease should consider stratifying patients based on Basal-like versus non-Basal-like gene expression profiles as this appears to be the main biological difference seen within TN breast cancer patients.

ORGANISM(S): Homo sapiens

PROVIDER: GSE41119 | GEO | 2014/07/29

SECONDARY ACCESSION(S): PRJNA256987

REPOSITORIES: GEO

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Project description:Breast cancer is a heterogeneous disease comprised of at least five major subtypes. Luminal subtype tumors confer a more favourable patient prognosis, which is in part, attributed to the Estrogen Receptor-alpha (ER) positivity and anti-hormone responsiveness of these tumors. Expression of the forkhead box transcription factor, FOXA1, also correlates with the luminal subtype and patient survival, but is present in a subset of ER-negative tumors. Similarly, FOXA1 is consistently expressed in luminal breast cancer cell lines even in the absence of ER. In contrast, basal breast cancer cell lines do not express FOXA1, and loss of FOXA1 in luminal cells increases migration and invasion, characteristics of the basal subtype. To delineate an ER-independent role for FOXA1 in maintaining the luminal phenotype, and hence a more favourable prognosis, we performed cDNA microarray analyses on luminal FOXA1-positive, ER-positive (MCF7, T47D) and FOXA1-positive, ER-negative (MDA-MB-453, SKBR3) cell lines in the presence or absence of transient FOXA1 silencing. This resulted in three FOXA1 transcriptomes: (1) a luminal-signature (consistent across cell lines), (2) an ER-positive signature (restricted to MCF7 and T47D) and (3) an ER-negative signature (restricted to MDA-MB-453 and SKBR3). Use of Gene Set Enrichment Analyses (GSEA) as a phenotyping tool revealed that FOXA1 silencing resulted in a transcriptome shift from luminal to basal gene expression signatures. FOXA1 binds to both luminal and basal genes within luminal breast cancer cells, suggesting that it not only transactivates luminal genes, but also represses basal-associated genes. From these results we conclude that FOXA1 controls plasticity between basal and luminal cells, playing a dominant role in repressing the basal phenotype, and thus tumor aggressiveness, in luminal breast cancer cells. Although it has been proposed that FOXA1-targeting agents may be useful for treating luminal tumors, these data suggest that this approach may promote transitions toward a more aggressive cancer. FOXA1 siRNA treated breast cell lines compared directly to nonspecific siRNA treated cell lines using Agilent 4X44 microarrays.

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Molecular Characterization of Basal-like and Non-Basal-like Triple-Negative Breast Cancers

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