Most cases of colorectal cancer risk factors develop from non-cancerous adenomatous polyps through a process called adenoma-carcinoma sequence, and the risk of developing colorectal cancer increases with the increase in size. Several epidemiological studies have indicated a number of genetic and environmental factors that can predispose to colorectal cancer. Following is a list of risk factors:
–Family history: Risk of developing colorectal cancer almost doubles in an individual with a history of colorectal cancer in first-degree relatives (parents, brother, sister, or child). The risk further increases several folds for such individuals if the first-degree relative gets diagnosed with the disease at an age </=60 years.
-Genetic Cancer Predisposition Syndromes: Some inherited cancer predisposition syndromes have been reported to be associated with a high incidence rate of colorectal cancer. Following are some examples: Lynch syndrome or hereditary non-polyposis colorectal cancer (HNPCC, generally caused by mutation in the MLH1 or MSH2 gene); Familial adenomatous polyposis (FAP, caused by mutations in the APC gene); Peutz-Jeghers syndrome (caused by mutation in LKB1); and Juvenile polyposis (caused by germline mutations in PTEN, SMAD4, BMPR1, or other genes yet to be identified).
Individuals with a history of colorectal cancer, adenomatous polyps, inflammatory bowel disease (ulcerative colitis or Crohn’s disease) are generally at higher risk of developing colorectal cancer.
-Age: Older age individuals are generally at increased risk of developing colorectal cancer.
-Lifestyle: Tobacco/cigarette smoking, excess alcohol consumption, and low physical activity have been reported to increase the risk of developing colorectal cancer.
-Diet: Consumption of red and processed meat, high-calorie diet, animal fat; and low intake of fruits and vegetables, fish, legumes, dietary fibers, and vitamins have been implicated to elevate the risk of colorectal cancer.
-Drugs: Use of certain drugs like aspirin, other nonsteroidal anti-inflammatory drugs (NSAID), and bisphosphonates have been reported to decrease the incidence of colorectal cancer.
Obesity, diabetes mellitus (especially type 2 diabetes), high waist girth are some other risk factors for colorectal cancer.
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