There are number of different factors working together in providing resistance to cancer in majority of people. In a previously held research, five kinds of anticancer mechanisms have been identified. The first type is immunological response which is influenced by genetic variations. It applies to virus associated cancers. The second mechanism is genetic, such as DNA repair mechanisms. The third mechanism is epigenetic which involves changes in gene expression, rather than changes in DNA itself. Like, in humans, defect in genetic imprinting can occur spontaneously and can increase the tumor incidence. Fourth anticancer mechanism is intracellular.
As part of an intracellular defense, a cell can trigger apoptosis, or cell death, if it detects extensive DNA damage, so that the cell does not replicate and spread the damage. The fifth known anticancer mechanism is intercellular which plays a major role in tumor resistance. Neighbouring cells that are in direct physical contact with each other can detect precancerous conditions in one another. They together act as a micro-environmental control system to prevent the development and progression of unhealthy cells. Along with the genetic and cellular factors, evolution seems to have favoured some relatively common resistance genes that protect majority of humans against cancer development.