The process and mechanism of carcinogenesis

Cancer occurrence process: • Normal cell stage: The tissues and organs of the human body are composed of normal cells, which carry out metabolism, proliferation, differentiation and other activities in an orderly manner under the regulation of genes. • Precancerous lesion stage: Under the action of some internal and external factors, such as long-term smoking, infection, bad eating habits, etc., some cells may have abnormal changes, and some precancerous lesions, such as intestinal metaplasia in the stomach, may occur, but it is not cancer at this time. • Carcinoma in situ stage: If the precancerous lesion continues to develop, the abnormal proliferation of cells is out of control, forming an early cancer that does not break through the basement membrane at the primary site, that is, carcinoma in situ, which generally does not metastasize at this stage. • Invasive carcinoma and metastasis stage: In the further development of carcinoma in situ, the cancer cells break through the basement membrane and invade the surrounding tissues to form invasive carcinoma. Subsequently, cancer cells can spread to other parts of the body through blood circulation, lymphatic system and other ways, forming metastases, leading to the development of cancer in many parts of the body. Mechanism of cancer: • Gene mutation: Internal and external environmental factors (such as radiation, chemical carcinogens, etc.) can lead to mutation of key genes (such as proto-oncogenes and tumor suppressor genes) in cells. The activation of proto-oncogenes and the inactivation of tumor suppressor genes make cell proliferation, differentiation, apoptosis and other processes out of control, and promote the formation and proliferation of cancer cells. Epigenetic changes, including DNA methylation, histone modification and other epigenetic changes, can affect gene expression, even if the genetic sequence is not changed, but can also make the normal regulatory mechanism of cells disorder, which is conducive to the generation and development of cancer cells. • Immune escape: Cancer cells can escape the recognition and attack of the body’s immune system through a variety of means, such as down-regulating the expression of molecules recognized by immune cells, making it difficult for the immune system to detect and eliminate them, so that they can continue to grow and reproduce in the body. • Abnormal tumor microenvironment: The microenvironment around cancer cells, including blood vessels, immune cells, fibroblasts and other components, has changed, which can provide nutritional support for cancer cells, assist their metastasis, and promote the occurrence and development of cancer. The following factors can affect the probability of cancer: Lifestyle factors • Smoking: It is an important risk factor for many cancers (such as lung cancer, bladder cancer, etc.). Carcinogens in cigarettes can damage cell DNA. • Alcohol consumption: Excessive alcohol consumption is associated with an increased risk of liver, stomach, esophageal and other cancers, and alcohol and its metabolites can cause cell damage. • Diet: Long-term high-salt, high-fat, low-fiber diet, excessive intake of processed meat, preserved food, etc., increases the risk of colorectal cancer, stomach cancer and other morbidity; while eating more vegetables, fruits and other foods rich in antioxidants has a certain protective effect. • Lack of exercise: Insufficient physical activity can lead to obesity, which is closely related to the morbidity of many cancers (such as breast cancer, endometrial cancer, etc.), and exercise helps to enhance the body’s immunity. Environmental factors • Chemical exposure: Long-term exposure to chemical carcinogens such as asbestos, benzene and formaldehyde can increase the risk of cancer, such as mesothelioma caused by asbestos exposure. • Radiation: including ionizing radiation (such as X-rays, gamma rays, etc.) and ultraviolet radiation. Excessive exposure can damage cell DNA and increase the risk of cancer, such as skin cancer caused by long-term excessive sun exposure. Infection factors • Viral infection: For example, human papillomavirus (HPV) infection is associated with cervical cancer and anal cancer; hepatitis B virus (HBV) and hepatitis C virus (HCV) infection can cause liver cancer. • Bacterial infection: Helicobacter pylori infection is closely related to gastric cancer and gastric lymphoma. Genetic factors • Some cancers are inherited in families, such as breast cancer, ovarian cancer (related to BRCA1/2 gene mutation), colorectal cancer (Lynch syndrome