There are three phases of development involved in the formation of cancerous growth. The second step is promotion which involves an action promoting the uncontrolled growth and proliferation of mutated cells. In time these cells loose their normal abilities and just reproduce. The third step is metastasis . This is the invasion of cancerous cells into nearby tissues as well as the migration of cancerous cells to other tissues via circulatory or transport systems.
Substances introduced to the body can cause mutation, promotion , or both.
A carcinogen which causes both is called a 'complete carcinogen'. Physical damage to tissues can cause cell proliferation. Some mutagens can damage surrounding tissues, leading to cell proliferation. This may also lead to cancer. Excess consumption of fat or salt, tobacco use, and alcohol consumption can raise susceptibility to chemical insult resulting in disease.