ABSTRACT
Many factors can contribute to carcinogenesis, including viruses, chemicals, radiation, diet, hormones, and genetical predisposition. In order to study carcinogenesis, the process has been historically and conceptually divided operationally into three steps: initiation, promotion, and progression. Proto-oncogenes are genes that have a normal role in cells and only become oncogenes when they are expressed inappropriately. The viral genome may integrate into the host cell genome, allowing permanent expression of the viral oncogenes, beginning the process of carcinogenesis. Genetical factors influencing carcinogenesis and cancer risk include heritable susceptibility factors, such as genetical polymorphisms in carcinogen metabolism, heritable defects in DNA repair genes, and even gender, ethnicity, and race. There are a number of types of genes in the tumor suppressor category. The most obvious are genes that “turn off” cell growth or increase cell death.
