In normal people, cells are constantly dividing and apoptotic, just like the alternation of old and new population on earth. This dynamic balance ensures the basic physiological state of organisms. If cells only divide without apoptosis, more and more cells will pile up. If they are still in a capsule and will not spread, they will form benign tumors; however, if tumor cells further evolve and acquire more malignant features, such as metastatic ability, cancer cells will spread to important organs of the whole body and eventually lead to biological death.
The hereditary expression of cancer is that the malignant characteristics of cancer cells can be transmitted between generations of cancer cells. The formation of cancer is related to two kinds of genes, one is oncogene, the other is tumor suppressor gene. When they mutate, their function deviates from the normal orbit, and cancer is triggered.
Oncogenes are derived from proto oncogenes. Proto oncogenes are found in the human body. They usually work normally and do not cause cancer. For example, c-myc is a proto oncogene, which is responsible for the synthesis of a certain amount of transcription factors. Transcription factor is an essential protein for DNA to RNA transcription. If the number of transcription factors is appropriate, it can not only make the cells divide normally, but also make the cells "die" after a certain period of survival. However, when proto oncogene c-myc mutates into oncogene, it will continuously synthesize such transcription factors, and excessive transcription factors will make cell division out of control.
Tumor suppressor gene is a kind of gene that controls cell life and prevents cell from surviving too long. If they are inactivated due to mutation, the cells will only divide without apoptosis, and the cells without any restriction will continue to proliferate, which may result in the formation of cancer. For example, there is a high incidence of childhood malignant tumor called retinoblastoma, which is caused by the inactivation of the tumor suppressor gene Rb1, which is usually inherited from parents.
There are two reasons for the inactivation of RB1 gene: one is that its structure has changed and mutated, which is genetic variation; the other is that its structure remains unchanged, but the promoter responsible for transcription initiation is methylated, which is epigenetic variation. Both types of mutations can cause retinoblastoma. Therefore, cancer is not only a genetic disease, but also an epigenetic disease. Only in this way can we really grasp the causes of cancer and find the measures to cure cancer.