The RAC1 mutation resulting in the substitution of proline for serine at residue 29 is the most frequently mutated amino acid in MM, after V600 mutations in BRAF and the glutamine (Q) substitution at position 61 in NRAS. RAC1 mutations are observed in 4 % of all melanomas and 9 % of sun-exposed melanomas and may occur either independently or in conjunction with BRAF and NRAS mutations, suggesting growth advantages distinct from activation of the MAP kinase signaling pathway [49, 50]. The gene discussed is RAC1; the disease is melanoma.