The PREX2 gene, which encodes a RhoGEF, is often mutated in metastatic solid tumours.146 The PREX2 S1113R mutant protein, present in patients with hepatocellular carcinoma, has been shown to promote the migration of Huh7 liver tumour cells in vitro.147RGS7, which encodes a Rho GTPase-activating protein, is a tumour suppressor that is mutated in melanoma. The gene discussed is PREX2; the disease is melanoma.