In vivo single-cell analysis revealed a time-dependent evolution from normal luminal MECs to luminal progenitor-like tumor cells with basal/mesenchymal transdifferentiation during murine BRCA1BLBC development.
Thus, we interbred mice expressing the CRE-recombinase with mice harboring loxP sites at TP53 and BRCA1 (K14-Cre; p53<sup>f/f</sup> Brca1<sup>f/f</sup>) to test the hypothesis that tissue-specific deletion of TP53 and BRCA1 would give rise to tumors reflective of human basal-like breast cancer.
Moreover, metformin treatment elicits a synergistic decline in the breast cancer-initiating cell population and its self-renewal capacity in BRCA1-mutated basal-like breast cancer cells with bone metastasis-initiation capacity that exhibit primary resistance to denosumab in mammosphere assays.
Breast cancers arising in the setting of the hereditary breast cancer genes BRCA1 and BRCA2 are most commonly classified as basal-like breast cancer (BLBC) or luminal breast cancer, respectively.
We identified two subsets of luminal progenitors (RANK(+) and RANK(-)) in histologically normal tissue of BRCA1-mutation carriers and showed that RANK(+) cells are highly proliferative, have grossly aberrant DNA repair and bear a molecular signature similar to that of basal-like breast cancer.
CINAHL® and PubMed databases, journals, and citation indices were searched using the key word basal-like in combination with breast cancer, epigenetic, treatment, subtype, risk factor, and BRCA1 to synthesize the literature on the multiple underpinnings of basal-like breast cancer.
Transient or stable exogenous S100A2 expression inhibits the growth of BRCA1 mutant and basal-like breast cancer cell lines, while short interfering RNA (siRNA) knockdown of S100A2 in non-tumorigenic cells results in enhanced proliferation.
DNA copy number analysis showed that cases with BRCA1 mutation were significantly associated with amplification both at 8q24 (frequencies: BRCA1 tumors 50%, BRCA2 tumors 32%, and wild-type tumors 9%) and regions of the X-chromosome specifically dysregulated in basal-like breast cancer (BLBC; BRCA1 62%, BRCA2 34%, and wild-type 35%).
Our working model is that the high frequency of basal-like breast cancer in BRCA1 mutation carriers is the result of a self-perpetuating triad of cellular phenotypes consisting of: (i) intrinsic defects in DNA repair and centrosome regulation that lead to genomic instability and increases spontaneous transformation; (ii) aberrant lineage commitment; and (iii) increased proliferation due to in large part to increased IGF-1 activity.
Protein expression and methylation of DNA repair genes hMLH1, hMSH2, MGMT and BRCA1 and their correlation with clinicopathological parameters and prognosis in basal-like breast cancer.
We demonstrate that this BRCA1-GATA3 repression complex is not a FOXC1-specific phenomenon as a number of other genes associated with BLBCs such as FOXC2, CXCL1 and p-cadherin were also repressed in a similar manner.
Predictive value of MGMT, hMLH1, hMSH2 and BRCA1 protein expression for pathological complete response to neoadjuvant chemotherapy in basal-like breast cancer patients.
Together, our findings establish that transcriptional upregulation of ΔNp63 proteins is critical for BRCA1 suppressor function and that defects in BRCA1-ΔNp63 signaling are key events in the pathogenesis of basal-like breast cancer.
BRCA1 mutations are often associated with basal-like breast cancer, which are also often negative for oestrogen receptor (ER), progesterone receptor (PR) and HER2.
The link between BRCA1 dysfunction and basal-like breast cancer or triple-negative breast cancer (TNBC) has been suggested; however, the associations of other factors involved in the Fanconi anemia (FA)/BRCA pathway with the pathogenesis of basal-like breast cancer remain unidentified.
Increased understanding of the genetic abnormalities involved in the pathogenesis of TNBC, BLBC and BRCA1-associated tumors is opening up new therapeutic possibilities for these hard-to-treat breast cancers.
TNBC is a heterogeneous disease that does not offer specific targets in the same way as HR-positive and HER2-positive breast cancers, and is similar to basal-like breast cancer and BRCA1-related breast cancer.
These data provide an example of a specific and recurrent oncogenic consequence of BRCA1-dependent dysfunction in DNA repair and provide insight into the pathogenesis of BBC with therapeutic implications.