How the Process Works There are anywhere from 50,000 to 100,000 genes within a human cell. But research suggests that not more than a hundred regulate cell growth or division. It is now also thought that we all carry normal cells that contain oncogenes in the chromosomes but that these oncogenes are never activated. They simply lie dormant throughout our lives.
In other cases, a mutation may occur because of some assault on the cell structure. Some stimulus or chemical agent turns on a "switch," several oncogenes are activated, and they set to work together to transform a normal cell into a cancer cell. This is thought to be at least a two-step process. First, the DNA must go through an initial change that makes the cell receptive. Then a subsequent change or set of changes in the DNA transforms the receptive cell into a tumor cell.
The big question is, what causes these changes in cellular DNA in the first place? There are several theories. One focuses on viruses, which can insert their own DNA into a cell's DNA and make the cell produce more virus-containing cells. Viruses may insert a viral oncogene or they might simply act as a random mutating agent.
There is also some evidence that an assault by a "single carcinogenic bullet" hitting the cell at just the right spot can make a cell become cancerous. But the theory that has gained a lot of support focuses on multiple "hits."
The Multiple Hit Theory According to this theory, all cancers arise from at least two changes or "hits" to the genes in the cell. These hits build up and interact over time. Eventually, a breaking point is reached and cancerous growth is switched on.
