Problems arise, however, when mutations convert the proto-oncogene to an oncogene, rendering Ras permanently active regardless of the signals the cell receives. How do tumor suppressors differ?

(A) Oncogene mutations were grouped together when ... (B) Incidence of BRAF mutations and co-occurring mutations in any RAS gene. (C) Incidence of co-occurring KRAS and PIK3CA mutations.

Two principal classes of these regulatory genes have been implicated in neoplastic development: proto-oncogenes and tumor suppressor genes. Proto-oncogenes encode proteins that stimulate DNA ...