Consistent with the notion that CDK5 promotes cell proliferation, inhibition of CDK5 activity using roscovitine, olomoucine, dinacilcib, CP681301 or expression of dominant-negative CDK5 constructs, or depletion using anti-CDK5 siRNAs decreased proliferation of in vitro cultured MTC, prostate, colon, colorectal and liver cancer cells, as well as proliferation of tumour cells in xenografts in vivo [59,62,77–79]. The gene discussed is CDK5; the disease is liver cancer.