Although no cancer-associated mutations in ERK itself have been identified to date, K-RAS and B-RAF are widely recognised oncogenes in which constitutively active mutations such as K-RASG12D and B-RAFV600E lead to colorectal cancer, breast cancer, leukaemia and melanoma through persistent activation of RAF–MEK–ERK and PI3K–Akt/mTOR signalling pathways [91,92]. The gene discussed is MAPK1; the disease is breast cancer.