The products of metazoan cell proto-oncogenes are generally key constituents of the cell signaling and gene expression machinery that regulate cell growth and proliferation. When mutated, amplified, or otherwise expressed in a dysregulated manner, these genes can become cellular oncogenes and their oncoprotein products drive tumorigenic cell growth. Examples of proto-oncogenes include the RAS genes, ERBB2, MYC, and ABL1. Certain viruses, or oncoviruses, have the capability to cause cancers through the action of viral genome-encoded oncoproteins that target metazoan cell factors or pathways.