The Cause of cancer

 The cause of malignant tumors is not fully understood. At present, the relatively clear factors related to cancer can be divided into two categories: exogenous and endogenous:

1. Exogenous factors

(1) Living habits Bad lifestyle habits such as smoking are closely related to the occurrence of cancer. About 1/3 of the patients who died from cancer are related to smoking, which is the main risk factor for lung cancer. Ingesting a large amount of strong alcohol can cause malignant tumors in the mouth, throat, and esophagus. High-energy and high-fat foods can increase the incidence of breast cancer, endometrial cancer, prostate cancer, and colon cancer. Drinking contaminated water and eating moldy food can induce liver cancer, esophageal cancer, and stomach cancer.

(2) Environmental Pollution and Occupational Pollution of air, drinking water, and food can cause serious harm to humans. The carcinogenic substances related to the environment that the World Health Organization has announced include: arsenic, asbestos, benzidine, 4-aminobiphenyl, chromium, ethylene estrol, radioactive radon, coal tar, mineral oil, coupled estrogen, etc. . These chemical or physical carcinogens in the environment enter the human body through the body surface, breath and digestive tract to induce cancer.

(3) Natural and biological factors Natural factors can also cause cancer. For example, ultraviolet rays can cause skin cancer under certain conditions. Biological factors are mainly viruses, of which 1/3 are DNA viruses and 2/3 are RNA viruses. DNA viruses such as Epstein-Barr virus are related to nasopharyngeal carcinoma and Burkitt lymphoma, human papilloma virus infection is related to cervical cancer, and hepatitis B virus is related to liver cancer. RNA viruses such as T-cell leukemia/lymphoma viruses are related to T-cell leukemia/lymphoma. In addition, bacteria, parasites, and fungi can cause cancer under certain conditions, such as Helicobacter pylori infection and gastric cancer. Schistosomiasis has been proven to induce bladder cancer, and Aspergillus flavus and its toxin can cause liver cancer.

(4) Chronic irritation and trauma. Trauma and local chronic irritation such as deep burn scars and chronic skin ulcers may become cancerous.

(5) Iatrogenic factors such as ionizing radiation, X-rays, radionuclides can cause skin cancer, leukemia, etc.; cytotoxic drugs, hormones, arsenic agents, immunosuppressants, etc. all have the possibility of causing cancer.

2. Endogenous factors

(1) Tumors that are directly inherited by genetic factors are only a few uncommon tumors. The role of genetic factors in most tumors is to increase the body's tendency to develop tumors and susceptibility to carcinogenic factors, which is the so-called genetic susceptibility. , Including chromosomal instability, genetic instability and microsatellite instability. For example, in familial colonic adenomatous polyps, due to germline cell APC gene mutations, most of them have colorectal cancer after 40 years of age; Brca-1 and Brca-2 mutations are related to breast cancer, and the incidence is more than 80%.

(2) Immune factors Congenital or acquired immunodeficiency is prone to malignant tumors. For example, patients with gamma protein deficiency are susceptible to leukemia and lymphohematopoietic tumors, and the incidence of malignant tumors in AIDS patients is significantly increased. However, most malignant tumors occur in people with "normal" immune functions. The main reason is that tumors can escape the surveillance of the immune system and destroy the body's immune system. The mechanism is not fully understood.

(3) Endocrine factors Abnormal hormone levels in the body are one of the tumor-inducing factors. For example, estrogen and prolactin are related to breast cancer, and growth hormone can stimulate the development of cancer.