Most cancers develop slowly from a complex sequence of events. DNA is the structure in our cells that builds our chromosomes, which serve as each cell's control center. DNA also contains genes, the basic unit of our heredity that tells our cells who we are and what to do. An alteration is usually caused by multiple factors which alter normal cell growth. Most scientists accept the theory of initiation and promotion.
Initiation means the DNA has converted, that something has caused mutations.
Promotion means something causes it to grow, but it can only grow as a cancer if the cell has undergone prior chromosomal change.