The fact that loss of MIB2-mediated increase in YAP/TAZ protein degradation had the same effect on YAP/TAZ protein levels and YAP/TAZ target gene activation as the loss of FAT1 indicates that loss of MIB2-mediated increase in YAP/TAZ protein degradation is a critical mechanism, by which mutations in FAT1 promote tumorigenesis and tumor progression. The gene discussed is WWTR1; the disease is neoplasm.