Over the last years, the study of loss of gene function has focused on RNAi. Recent advances in genome editing have identified a powerful tool, CRISPR/Cas9, that dramatically improved target specificity and complete functional knockout. Its high potential to accelerate life sciences research has led several labs to try to implement it in various organisms. CRISPR/Cas9 applications include cancer modeling. Cancer is basically a disease of uncontrolled cell division. The spindle assembly checkpoint is the main control mechanism of mitosis and ensures correct cell division. Bub3 and Spindly proteins are key components of this pathway by activating or silencing it, respectively. Using CRISPR/Cas9 technology, we intend to create clones of human tumor cells, with Bub3 and Spindly gene knockout. Phenotypic changes and effects on cell viability, proliferation and apoptosis will be evaluated. Inhibition of Bub3 and Spindly by siRNA will be included, comparing CRISPR and RNAi. The therapeutic potential of knockout in combination with paclitaxel will be assessed.