Tumor suppressor genes block cell division, or instruct cells to die when appropriate. Even when cancer-related mutations are present in a cell, cancer does not always develop. The reason for this is not known. The majority of all cases of cancer, however, are related to acquired mutation. Each time a body cell divides, the DNA must be replicated, so that each daughter cell receives a complete copy of the genetic material.
Mistakes can and do occur during the DNA replication process.
Most mistakes are corrected, but occasional mistakes slip past the cell's 'proof-reading' mechanisms, resulting in mutation. Certain agents can damage DNA, or interfere with accurate replication of DNA, increasing the likelihood of mutation. A risk factor is any characteristic associated with an increased likelihood of developing a disease. Risk factors are different for different types of cancer. Although the relationship between specific risk factors and acquired gene mutations is not always clear, risk factors are thought to increase the likelihood of cancer by increasing the likelihood of DNA damage.