The best-studied Rho GTPases—Rac1 and RhoA—are often mutated in various types of cancer.136RAC1 is the third most frequently mutated gene in melanoma after BRAF and NRAS. 137 The RAC1 P29S driver mutation, which results from a C > T transition in response to UV damage, generates a more active form of Rac1. The gene discussed is RHOA; the disease is cancer.