Three key genetic mechanisms have a role in human carcinogenesis

Activation of proto-oncogenes, resulting in hyperactivity of growth-related gene products (called oncogenes)

Mutation of genes, resulting in the loss or inactivity of gene products that would normally inhibit growth (called tumor-suppressor genes)

Mutation of genes, resulting in an overexpression of products that prevent normal cell death or apoptosis, thus allowing continued growth of tumors