ANALYSIS OF GENOMIC INSTABILITY AND INVASIVENESS IN DUCTAL CARCINOMA IN SITU

Abstract

Ductal carcinoma in situ (DCIS) is a nonobligate precursor of invasive breast cancer. If left untreated, 14 to 53% of DCIS cases would progress to invasive breast cancer although there is currently no accurate way to identify indolent versus aggressive DCIS. Accurate prediction of DCIS behavior would greatly reduce patient suffering and medical costs. The goal of this study was to identify prognostic biomarkers by evaluating two types of biomarkers: those related to genomic instability involving the Nucleotide Excision Repair (NER) pathway and those indicative of cell behaviors involving Epithelial to Mesenchymal Transition (EMT). Using a novel tissue-engineering system established in the Latimer laboratory, DCIS model systems were created. We previously established that stage I breast cancer had significantly lower NER function and gene expression than non-diseased breast explants. This project examined the functional NER capacity of these novel DCIS primary and extended explants using the unscheduled DNA synthesis assay. DCIS was not statistically different than the non-diseased breast NER capacity although was significantly higher than stage I breast cancer explants. The invasive capacity for DCIS explants was evaluated using the transwell assay and differential expression of five EMT genes. Pure DCIS explants had a significantly lower invasiveness than those explants synchronous with invasive breast cancer. Invasive DCIS cells were separated from noninvasive DCIS cells from selected explants using the transwell assay. Invasive DCIS cells had a lower functional NER capacity/higher genomic instability compared to noninvasive DCIS cells from the same tumor. Overall expression of NER genes was higher in DCIS explants than non-diseased breast explants and stage I breast cancer using RNA sequencing. The expression of the NER genes was downregulated in invasive DCIS cells relative to isogenically matched noninvasive DCIS cells, consistent with the functional data. The protein data of NER genes in both DCIS explants as well as isolated invasive and noninvasive cells showed a concordance with the gene expression as performed by western blotting. Invasive DCIS cells and DCIS that is synchronous with invasive breast cancer had lower overall NER gene expression. Therefore, NER with selected EMT genes could provide a panel of novel prognostic biomarkers for DCIS alone or in combination with existing markers.