Abstract A55: Genes regulating the progression of human ductal carcinoma in situ to invasive breast cancer

Introduction: The progression from a localized ductal carcinoma in situ (DCIS) into an invasive breast cancer (IBC) represents a major and life-threatening alteration. Unfortunately, our ability to predict which patients will and will not progress to invasive breast cancer is rudimentary. If we are to develop better tests (i.e., prognostic markers) to determine who will progress and increase our understanding of how progression occurs, we will be able to develop tests that predict progression and uncover new and more effective therapies for breast cancer patients. In this study, we assessed the change of the gene expression profiles during the progression of DCIS into IBC and identified some candidate genes which putatively regulate this lethal alteration. Method: The genetic changes responsible for the progression of DCIS into IBC were assessed by comparing gene expression profiles in five separate but complimentary cohorts of human DCIS vs. IBC by microarray analysis, and the candidate genes were identified. For the functional studies of the candidates in regulating this malignant progression, we knocked down the expression of 10 genes, which appeared to be downregulated in IBC (hypothesizing that they function to suppress invasion and predicting that depleting them in DCIS.COM would promote invasion-related behaviors) using lentiviral constructs of short hairpin RNA. The transduced cell line was a MCF10A-derived cell line, DCIS.COM, which appeared a DCIS-like phenotype in xenograft. The transduced DCIS.COM cell lines were then transplanted into the primary mammary intraductal nipple of immune-compromised mice (MIND xenograft), and grew them for 5–10 weeks to assess the effects of knocking those 10 genes out on the invasive breast cancer development. Results: Through the microarray studies, we identified over 2500 genes differentially expressed in the epithelial cells of DCIS and IBC cancers, and picked 35 genes of interest. The transduced (shRNA) DCIS.COM cell lines of 10 putative inhibitors of breast cancer invasion were evaluated for growth and progression in vivo in the MIND xenograft. Among the assessed 10 genes, six genes resulted in rapid progression to large invasive tumors at 10 weeks, and especially two of them showed drastic invasive tumor growth at only 5 weeks (CSTA and FAT1). This result confirmed in hDCIS.01, another human DCIS cell line. In vitro assays for migration and invasion demonstrated that delpetion of CSTA and FAT1 gene expression resulted in elevated invasiveness in DCIS cell lines. Conclusions: Our microarray assay revealed that the genetic alteration in the mammary epithelium is one of possible mechanisms to regulate the progression of human DCIS to IBC. The gene expression signature generated from this microarray study represents a unique and valuable resource to support studies of the progression of DCIS to IBC. The MIND xenograft data demonstrated that the screened genes among the established gene signatures are deeply involved in changes from DCIS into IBC, which strongly supports the hypothesis of genetic alteration in governing the malignant conversion of breast cancers. Especially, the CSTA and FAT1 appeared to be as strong inhibitors of invasive cancer development. The other candidate genes, which appeared to be modulated in the progression of DCIS to IBC will be assessed with similar strategies. This study is a prerequisite for the development of a prognostic signature to predict progression, and will identify genes for novel targeted therapies to suppress invasion, thereby benefiting patients with DCIS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A55.