PO-334 Distribution of copy number alterations defines clonal populations involved in the evolutionary transition from adenoma-to-carcinoma in colorectal cancer

Abstract

screening. DCIS is usually treated by surgery combined with radiotherapy, which can have a large impact on the life of patients. However, there is little to no evidence that treatment of low and intermediate grade DCIS reduces mortality, while women diagnosed with DCIS do perceive their risk of dying the same as patients with invasive disease. To reduce the negative perception and the overtreatment of DCIS, but assure proper treatment for high risk DCIS, it is critical to understand the progression of DCIS and which genetic factors initiate DCIS formation. Material and methods To understand the initiation and progression of DCIS, existing non-germline mouse models are used for establishing genetic DCIS models. To generate these, multiple genes were selected from previous work and literature which are suspected to play a role in DCIS initiation. Firstly, PIK3CA(H1047R) and Myc were incorporated in lentiviral vectors and injected in the mammary gland of immunocompetent mice, while Trp53 was conditionally knocked out by introducing a Cre lentiviral vector in the mammary gland of FVB Trp53 F/F mice. In addition, these genetic aberrations were investigated in combinations. To further characterise human DCIS we derived fresh patient DCIS material to create in vitro tumouroid cultures, which we transplanted into NSG mice. Furthermore human DCIS cell lines will be stained using multiple fluorescent markers simultaneously to create a coloured 'cell library'. These will be injected intraductally and followed by intravital imaging to assess the dynamics of progression to an invasive breast cancer. Results and discussions We have successfully shown that it is possible to propagate breast cancer cell lines and tumouroid lines, as well as DCIS cell lines in vivo using intraductal injections. Modifications of these lines are possible using lentiviral vectors, also allowing for intravital imaging. Besides this, the genetic models are initiated and primary DCIS tumouroids have been cultured in vitro successfully. Conclusion Generating these models will provide a better understanding of the biological processes underlying DCIS initiation and progression. This knowledge can then be used to predict DCIS evolution and distinguishing patients with high risk DCIS from low risk DCIS, which will aid in better care. Introduction Alterations in DNA repair pathways are thought to fuel tumour progression. Mismatch Repair (MMR) deficient cancers show peculiar biological features such as an indolent progression and a resolute therapeutic response to checkpoint inhibitors. The genomic and biological bases of the peculiar clinical features are poorly understood. Further progress in this area is limited by the paucity of models to study the impact of MMR genes inactivation at the genomic and biological levels. To address this issue we developed a bioinformatic workflow to monitor the neoantigen repertoire induced by inactivation of the Mlh1 gene (a key player of the MMR machinery), in murine cell lines. Material and methods We inactivated Mlh1 ...