→ Defined as stable and heritable change → This is a rapid, IRREVERSIBLE process that can result to carcinogen-induced mutational event

Initiation phase → The initiating agent or toxicant will interact with the normal cell → it will cause DNA damage or alteration of DNA structure (mutation) → then it will become initiated cells → There are instances/ processes that the body can initiate repair on DNA level (excision repair, nucleotide repair, recombinational repair) → However if it is beyond repair → The initiated cell cannot be fixed. We cannot reverse the initiated cells