What is the double hit theory in oncology? How to explain it?

This is the "two strikes theory" of tumor canceration.

The following is the "two strikes" theory that I helped you look up in the encyclopedia. It was first put forward in 197 1. Knudson believes that the occurrence of retinoblastoma in children is the result of two mutations through the analysis of its incidence. The first mutation occurred in germ cells and the second mutation occurred in somatic cells after birth. A large number of molecular biology studies have confirmed this "two strikes" proposed by statistical analysis. The essence of "Double Strike" is that a pair of alleles of retinal cell sensitive gene (Rb 1) have mutated. In hereditary cases, because one Rb gene has been inactivated in germ cells, it is necessary to inactivate the Rb gene in another somatic cell after birth to form a tumor, so the onset is early. However, in sporadic cases, it takes twice inactivation of somatic Rb gene to form a tumor, so the onset is late. The genetic susceptibility of tumors may be related to the inactivation of anti-cancer genes in some hereditary diseases or defects. Inactivation of homozygous rb gene (that is, both alleles of Rb gene are inactivated) occurred not only in retina, but also in other tissues of the patient, and both Rb alleles were inactivated at the same time, indicating that normal Rb gene has anticancer effect in different tissues. At present, Rb gene inactivation has been found in many common human malignant tumors. Recently, it has been found that p53 gene in patients with Li-Fraumani syndrome is also a species mutation, suggesting that p53 gene may also be influenced by genetic tendency. Therefore, the theory of "two strikes" may have certain guiding significance. The theory of "two strikes" is mainly applicable to tumors with genetic tendency, such as retinoblastoma, nephroblastoma, chondrosarcoma and neuroblastoma. For most sporadic tumors, it is more likely to be considered as the cumulative result of various genetic changes.