Introduction The proportion of patients with metastatic with colorectal cancer (CRC) who are cured of their disease is increasingly, but still low. The spread of cells from the primary tumour to distant sites is a complex process. Two of the key issues to be addressed to understand and prevent metastasis are the development of robust model systems and the robust identification of the molecular drivers.

Method In this study, we used the novel technique of mouse endoscopy to introduce a syngeneic CRC cell directly under the submucosa of the large intestine of mice. A whole genome CRISPR/Cas9 screen was then performed using the GeCKOv2 library and we take a non-hypothesis driven approach to screen 20 611 genes for drivers of CRC metastasis.

Results In the metastatic lesions of the mice, a median of 2548 genes were identified. FOXF1 was frequently targetted from this screen and significantly down-regulated in human lung and liver metastasis specimens. Whole transcriptome profiling identified that FOXF1 functions through inhibition of MTOR signalling and inhibition of this pathway significantly reduced metastasis outgrowth in murine models.

Conclusion Genetic screens provide a comprehensive approach to understanding the drivers of metastasis. These assays allow the analysis of the function of a large number of genes simultaneously to identify those which are important for metastasis. In our approach, using an endoscopically guided orthotopicaly transplanted CRC model, we have identified 6 genes which had good evidence of modulating metastasis risk in our model system and were significantly downregulated in human metastasis cohorts. Several of these are particularly functionally interesting, including FOXF1, MDC1 and SEZ6L. By identifying several genes that modulate the probability of metastasis, we have developed a greater understanding of metastasis biology and identified FOXF1 as a biomarker of prognosis from CRC.

Disclosure of Interest None Declared