What are the main causes of colon cancer?

Some epidemiological studies on colon cancer have shown that social development, lifestyle and dietary structure are closely related to colon cancer, and there are phenomena suggesting that there may be differences in environmental and genetic factors affecting the incidence of colon cancer in different parts and age groups. Environment (especially diet), genetics, physical activity, occupation, etc. are possible etiological factors affecting the incidence of colon cancer.

1. Dietary factors

Epidemiological studies have shown that more than half of tumor incidence is related to environmental factors and lifestyle, and a few of these environmental factors are related to diet and nutrition to a certain extent. Therefore, dietary factors are considered to be extremely important factors in the incidence of tumors.

(1) Mechanism of action of high fat, high protein and low fiber:

It can be summarized as follows: ① It affects intestinal lipid metabolism. A high-fat diet increases the activity of 7a-dehydroxylase, leading to an increase in the formation of secondary bile acid, while cellulose has the opposite effect. It reduces the concentration of deoxybile acid in the intestine by inhibiting reabsorption, dilution, adsorption, and chelation, increases the solid phase in the feces, and promotes excretion; some dietary factors (such as calcium ions) can reduce the levels of intestinal ionized fatty acids and free bile acids, both of which have a damaging effect on the intestinal epithelium; inhibit the degradation of intestinal cholesterol. Milk, lactose, and galactose have an inhibitory effect on bile ane redox. ② Cellulose also has the effect of changing intestinal flora, affecting the structure and function of intestinal mucosa, affecting the growth rate of mucosal epithelial cells, regulating intestinal pH, and strengthening the mucosal barrier through mucin, reducing the damage of intestinal toxic substances to the intestinal epithelium; ③ High fat and some carbohydrates can increase the activity of intestinal cell enzymes (such as glucuronidase, ornithine dehydroxylase, nitroreductase, azooxidase, lipoxygenase, cyclooxygenase), and promote the production of carcinogens and co-carcinogens. ④ Influence of biological macromolecule activity: When the cytoplasm is acidified, DNA synthesis is inhibited and the cell cycle is prolonged.

(2) Vitamins:

Case-control studies have shown that carotene, vitamin B2, vitamin C, and vitamin E are all associated with a reduced relative risk of colon cancer, and the relationship is dose-response. Vitamin D and calcium have a protective effect.

(3) Onions and garlic:

The protective effect of garlic on the body has been widely recognized, and the inhibitory effect of garlic on tumor growth has been confirmed many times in experiments. Garlic oil can significantly reduce the damage to colon mucosal cells caused by dimethylcholanthrene, and can reduce the incidence of colon cancer in mice by 75%. The results of a case-control study showed that the risk of colon cancer in people with high intake of garlic foods is 74% of that in the low intake group.

(4) Salt and preserved foods:

The relationship between salt intake and gastric cancer, colon cancer, and rectal cancer. The high salt intake group showed that the relative risk of the three cancers increased. The case-control study results showed that the excess risk of colon cancer in those who consumed pickled food more than three times a week was 2.2 times that of those who consumed pickled food less than once (P<0.01), 2.1 times for left colon cancer, and 1.8 times for right colon cancer. The explanation for this risk factor may be related to the carcinogens produced during the food pickling process, and high salt intake may be a concomitant state.

(5) Tea:

Tea polyphenols are a strong antioxidant that can inhibit the carcinogenic effect of carcinogens. According to the results of a case-control study, the risk of colorectal cancer in people who drink tea (green tea or black tea) more than three times a week is 75% of that in those who drink tea less than once a week, but the correlation with the colon cancer group is not close. In the past 10 years, studies have shown that tea drinking is significantly negatively correlated with the risk of colon cancer, but there are also reports of opposite results. Due to the small number of population studies on the protective effect of tea drinking against colon cancer, it is currently difficult to evaluate the role of tea drinking in the development of human colon cancer. The relationship between coffee and colon cancer is still difficult to determine.

(6) Trace elements and minerals:

① Selenium: The mortality rate of various cancers (including colon cancer) is negatively correlated with the local dietary selenium intake and soil selenium content. It is speculated that selenium and potassium are associated with a low risk of colon cancer. However, some believe that these factors may only be some accompanying factors and do not directly affect the risk of colon cancer in the population. ② Calcium: Animal experiments have shown that calcium can improve the toxic effects of deoxycholic acid on the intestinal epithelium. Some scholars believe that increased concentrations of bile acids and free fatty acids in the intestine can promote the occurrence of colon cancer, and calcium can combine with them to form insoluble saponification products, which reduces their irritation and toxic effects on the intestinal epithelium. Some epidemiological studies have also suggested that calcium intake can protect against the occurrence of colon cancer.

2. Occupational factors and physical activity

Colon cancer is more common among workers who produce insulating asbestos, and animal experiments have confirmed that swallowed asbestos fibers can penetrate the intestinal mucosa. In addition, the metal industry, cotton yarn or textile industry, and leather manufacturing industry. It has been confirmed that acrylonitrile, a compound often used in the production process of plastics, synthetic fibers, and rubber, can induce stomach, central nervous system, and breast tumors, and textile workers who are exposed to this substance have a higher incidence of lung cancer and colon cancer. Despite this, colon cancer is generally not considered an occupational disease.

In the analysis of occupational physical activity, it was found that the risk of colon cancer for those who sit for a long time or often is 1.4 times that of those who sit in some occupations with greater physical activity, and is closely related to cecal cancer. The results of case-control studies have shown that moderate-intensity physical activity plays a protective role in preventing colon cancer (especially colon cancer).

3. Genetic factors

It is estimated that genetic factors may play an important role in at least half of colon cancer patients, of which 1% are patients with familial polyposis and hereditary non-polyposis colon cancer syndrome. More than half of patients with hereditary familial polyposis may develop malignant tumors after the age of 59. In addition, most patients with familial polyposis develop left-sided colon cancer, while patients with hereditary non-polyposis syndrome often suffer from right-sided colon cancer.

Through a case-control pedigree survey of the entire population (1,328 families of probands with colon cancer and 1,451 families of population controls), the results showed that the incidence of colon cancer in first-degree relatives of different proband groups was significantly higher than that in second-degree relatives. The age of the proband at diagnosis of colon cancer is related to the risk of colon cancer in first-degree relatives. The younger the proband, the greater the relative risk of colon cancer in first-degree relatives. The relative risk of first-degree relatives of probands with colon cancer under 40 years old is 6 times that of those over 55 years old. Family members (first-degree relatives) with a family history of colon cancer, especially those with a colon cancer onset age of under 40 years old, should be given high attention.

4. Disease factors

(1) Intestinal inflammation and polyps:

Chronic intestinal inflammation and polyps, adenomas, and extensive ulcerative colitis for more than 10 years: The risk of developing colon cancer is several times higher than that of the general population. The chance of ulcerative colitis patients with severe atypical hyperplasia developing colon cancer is about 50%. Obviously, the risk of colon cancer in ulcerative colitis patients is higher than that of the general population. Data from my country suggest that the risk of colon cancer in patients with onset for more than 5 years is 2.6 times higher than that of the general population, and the relationship with rectal cancer is not close. For those with localized and intermittent lesions, the risk of colon cancer is low.

Crohn's disease is also a chronic inflammatory disease that often affects the small intestine and sometimes the colon. There is increasing evidence that Crohn's disease is associated with the development of colon and small intestinal adenocarcinoma, but not to the same extent as ulcerative colitis.

(2) Schistosomiasis:

Based on the retrospective survey of cancer deaths in Zhejiang Province from 1974 to 1976, the survey data of malignant tumors in China from 1975 to 1978, and the Chinese Schistosomiasis Atlas, the correlation between schistosomiasis endemic areas and the incidence and mortality of colon cancer was explored. There is a very significant correlation between the incidence of schistosomiasis and the mortality of colon cancer in 12 provinces, municipalities, and autonomous regions in southern my country and 10 counties in Jiaxing, Zhejiang Province. This suggests that in areas where schistosomiasis is severely endemic in my country, schistosomiasis may be related to the high incidence of colon cancer. However, there is little evidence from epidemiological studies on the correlation between colon cancer and schistosomiasis. For example, in Jiashan County, Zhejiang Province, where schistosomiasis is gradually being controlled, the mortality rate of colon cancer and the incidence of schistosomiasis in this area were once the highest in my country, and the infection rate of schistosomiasis has dropped significantly. However, according to the results of recent surveys, the epidemiological and pathological research reports on the canceration of colon polyps also believe that the canceration of polyps has nothing to do with the presence or absence of schistosome eggs in the polyps. In addition, the results of the colon cancer survey conducted in the two regions did not support that schistosomiasis is a risk factor for colon cancer. The case-control study found no correlation between a history of schistosomiasis and the incidence of colon cancer.