Abstract Serrated colorectal cancer (CRC) is an aggressive and treatment-resistant form of colorectal carcinogenesis that accounts for one-fourth of the patients with CRC1. At the molecular level, serrated CRC is characterized by epigenetic modifications termed the CpG Island Methylator Phenotype (CIMP) and the presence of somatic mutations that activate the mitogen-activated protein kinase (MAPK) pathway1,2,3. The BRAFV600E is an early genetic change in serrated polyps, but it is not sufficient to drive tumor formation. Combinations of mutations and epigenetic modifications in P16INK4A, MLH1, ZNFR3, RNF43, and TGFBR2 are often seen in most patients4. Therefore, a combinatorial approach to develop BrafV600E-driven serrated CRC organoids harboring a variety of the above mutants will enable in vitro studies of the tumorigenic potential of each combination as well as allow engraftment into animals. In turn, the latter will allow for applying preclinical in-vivo pharmacology modalities in vitro, thereby bypassing the time required to create a specific knock-in/out strain for each genetic modification desired. Here, we describe a pipeline to directly genetically manipulate specific organoid systems in vitro. We first established organoid cultures from the small and large intestine of unique Tet-inducible RNAi mice where efficient gene knock-down can contribute to microsatellite instability. Using CRISPR/Cas9, we then edited these to generate CRC organoid models containing the BrafV600E mutation in combination with knock outs or knock-ins of cell cycle regulators and negative regulators of the Wnt pathway. These deficiencies mimic the progressive mutational changes upon acquisition BrafV600E. Our data lay the groundwork for future use of RNAi technology in combination with sequential gene editing for in vitro pharmacology and modeling diseases with complex genetic architecture both in vitro and in vivo. Citation Format: Prem K. Premsrirut, Huaien Wang, Eduardo J. Garcia Reino, Isabella Breen, Ana A. Vasileva. Utility of intestinal organoids to model serrated colon cancer in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 946.