Scientists are not certain how colorectal cancer begins but some controllable and uncontrollable risk factors have been associated with the disease. The risk of colorectal cancer rises with age. More than 90 percent of cases affect people age 50 and older. Other factors that increase the chance of developing colorectal cancer:

• Personal medical history of colon, rectal, ovarian, endometrial or breast cancers.
  
  
• Family history of colorectal cancer. Individuals who have two or more close relatives with colorectal cancer account for about 20 percent of patients with colorectal cancer, according to the American Cancer Society (ACS).
  
  
• Colon polyps.
  
  
• Chronic inflammatory bowel diseases. These include ulcerative colitis, or ulcers in the lining of the colon, and Crohn’s disease, an inflammation of the gastrointestinal tract.
  
  
• Diabetes.  Recent studies have found a correlation between this metabolic disorder and colorectal malignancy. Individuals with diabetes have a 30 to 40 percent increased risk of colorectal cancer, according to the ACS. Researchers suspect that certain lifestyle habits (e.g., diet) may be associated with both diabetes and colorectal cancer.
  
  
• Hereditary colorectal disorders. Inherited gene mutations account for 5 to 10 percent of people with colorectal cancer.  Genetic tests can detect these defects in DNA. The ACS recommends that people with a family history of colorectal cancer ask their physician about genetic counseling and testing. Inherited colorectal disorders that can be detected with genetic testing include:
  
  
• • Familial adenomatous polyposis (FAP). A condition in which hundreds of polyps develop. This usually develops between age 5 and 40. Most people with FAP will develop colorectal cancer by age 40 unless they have their colon removed.
    
    
  • Hereditary nonpolyposis colon cancer  (HNPCC). Also know as Lynch syndrome, this condition occurs at a young age causing few rather than hundreds of polyps. Individuals with this condition have an 80 percent chance of developing colon cancer by age 75. HNPCC also increases the risk of other cancers, including stomach, pancreas and endometrial cancer in women.
    
    
  • Peutz-Jeghers syndrome (PJS).This condition can cause the development of numerous polyps in the small intestine and colon. People who have been diagnosed with PJS have a 39 percent risk of developing colon cancer by age 64.
    
    
  • Juvenile polyposis. A genetic condition that causes polyps to grow throughout the intestinal tract beginning in early childhood. These individuals have a greater risk of developing colon cancer by age 60.
    
    
• Ethnicity. Jews of Eastern European descent (Ashkenazi Jews) appear to have more colorectal cancer, perhaps due to an identified genetic mutation.
  
  
• Night-shift work.  People who work consistently at night may have a higher risk of colorectal cancer. One study found a higher incidence of the disease in individuals who worked a night shift at least 3 nights a month for 15 months or more. Scientists suspect the greater risk may be related to melatonin levels in the body that may change according to light exposure. Additional research is necessary to confirm the association with colorectal cancer.
    

The Centers for Disease Control and Prevention (CDC) lists the following as lifestyle risk factors for colorectal cancer. Individuals can change these lifestyle habits to reduce their risks:

• Lack of regular physical activity
• Diet high in fat, particularly from animal sources
• Diet low in fiber, vegetables and fruits
• Obesity
• Heavy consumption of alcohol
• Use of tobacco