Trametinib treatment decreased the growth of CICWT tumors compared to vehicle treatment (p = 0.01), but had little effect on CICKO tumors. Indeed, trametinib-treated CICKO tumors grew at comparable rates to vehicle-treated CICWT or CICKO tumors (Figure 3H). Based on these observations, we concluded that CICKO reduces sensitivity to trametinib treatment in vivo.