Causes of Colon Cancer

General Considerations: Colon cancer is the second most common cancer and cancer killer in the adults. It develops in approximately 6% of Americans and 40% of those die of the disease. Colon cancer when seen through an instrument called colonoscopy appears like bulky out growth protruding into the colon lumen or it may be like a constricting ring narrowing the colon lumen.

Followings are considered to be the possible causes of colon cancer:

• Polyp- an outgrowth in colon lumen that can transform into the colon cancer
  
• Loss of function of tumor suppressor gene- a tumor suppressor gene is a part on DNA suppressing the growth of tumor cells
  
• Activation of oncogenes- oncogenes are genes involved in proliferation of tumor cells
  
• Inherited syndromes
  

A polyp is an outgrowth in the bowel wall protruding into the bowel lumen. It is formed in the bowel wall because of excessive proliferation of normal cells. It is one of the major causes of colon cancer. The current thought is that the majority of the colon cancers arise from the malignant change of a polyp i.e. when cells in the polyp grow excessively and immaturely, they can give rise to colon cancer. Genes are parts of DNA that control different body functions like growth and differentiation of cells. Tumor suppressor genes normally suppress the growth and division of our body cells. When they lose function properly, cells grow in an uncontrolled way thus leading to cancer. There are many such tumor suppressor genes whose dysfuntining is an important cause of colon cancer. Oncogenes are genes which when activated cause the growth of cancer cells. Activation of many such genes is one of the causes of colon cancer. Up to 5% of the colon cancers are caused by inherited germ line mutations resulting in polyposis syndromes- syndromes having many polyps in colon¹.

Risk Factors

It is thought that there are many risk factors which coexist with underlying cause of colon cancer. Early detection of these factors has an impact on screening strategies. However, 75% of all cases of colon cancer are seen in those people with no known predisposing factors. These risk factors include the followings:

• Age
  
• Family history of cancer
  
• Inflammatory bowel disease
  
• Dietary factors
  
• Others
  

The incidence of colon cancer increases swiftly after the age of 45 years, and 90% of the cases occur after the age of 50 years. A family history of colon cancer is seen in 20% of the patients with colon cancer. Hereditary factors are the cause of colon cancer in 20-30% of the cases. Inflammatory bowel disease is another important cause of colon cancer, the risk of colon cancer tends to increase after 7-10 years of disease onset. Chronic treatment with 5-aminosayliclic acid and folic acid in patients with inflammatory bowel disease is associated with low risk for development of colon cancer. The diet rich in fats or red meat increases the risk of colon cancer while diet containing fibers, fruits, grains and vegetables is associated with decrease risk of colon cancer. The incidence of colon cancer is higher in blacks than in whites. Diabetes, metabolic syndrome, obesity and cigarette smoking are associated with modest increase in cancer risk. Metabolic syndrome refers to group of risks that cause heart diseases and diabetes.

Clinical Findings

The clinical symptoms and signs of colon cancer depend upon the location of the cancer. Generally followings are the clinical features of a colon cancer²:

• Anemia
  
• Fatigue
  
• Generalized weakness
  
• Blood in stool
  
• Alternating bowel habits
  
• Constipation
  
• Feeling of incomplete evacuation of bowel after defecation
  
• Colicky abdominal pain
  
• Loss of appetite
  
• Weight loss
  

Left sided colon cancer tends to obstruct the bowel and patient presents with alternating bowel habits, constipation and colicky abdominal pain- the pain that comes and goes. Right sided colon cancer tends to bleed and it presents with features of anemia, fatigue, weakness and a swelling in right iliac fossa^1,2,3.

Investigations

Following investigation are carried out for diagnosis and selection of treatment option of colon cancer^2,3 :

• Stool examination for presence of occult blood
  
• Colonoscopy and biopsy of the cancer is the gold standard test for diagnosis of colon cancer
  
• Complete blood count to check for the anemia
  
• Liver function tests
  
• Ultrasonography of abdomen and pelvis to confirm the spread of cancer
  
• CT scan of chest, abdomen and pelvis to look for spread of colon cancer
  
• Carcinoembryonic antigen (CEA) levels- a tumour marker
  

  Colon Cncer and Polyp

  
  

   

  Fig: Locations of Colon Cancer⁵
  

   

  

  Locaton of Colon Cancer

  
  

   

  Fig: Clonoscopic view of colon cancer⁶
  

   

   

Prevention of Colon cancer

Followings are some handy points that can prevent occurrence of colon cancer²:

• Use of aspirin prevent the colon cancer development
  
• Oral folic acid and oral calcium supplements reduce the risk of colon cancer
  
• Antioxidant vitamins have some role in prevention of colon cancer
  
• Use of estrogen replacement therapy in females reduces the risk of colon cancer
  
• Avoid fatty foods and red meat
  
• Use fibers, grains and vegetables more
  
• Regular screening via colonoscopy for early detection of causes of colon cancer
  

Treatment Options

Following are the available options for treatment of colon cancer:

• Surgery
  
• Chemotherapy
  
• Radiotherapy
  

Surgery:

Surgery is the treatment of choice for early stages of colon cancer. During surgery the involved part of the colon is resected. For advanced stages of colon cancer when it spreads to other sites, a palliative surgery can be done to relieve the pain and other symptoms of colon cancer. If the cancer spreads to liver, surgical resection of some part of it can be done².

Chemotherapy:

It means treatment of colon cancer by giving some chemical drugs that can kill the cancer cells. Usually, chemotherapy is used after surgery to kill the remaining cancer cells. The drugs which are used in colon cancer treatment include folinic acid, 5-Flourouracil and irinotecan².

Radiotherapy:

As colon cancer is radio-resistant radiation has no significant role in treatment of colon cancer. It is used externally or internally to relieve the pain of colon cancer as it reduces the size of cancer cells^2,4.

References

1. Papadakis MA, Macphee SJ, editors. Current Medical Diagnosis and Treatment.52^nd ed. New York: Mc Graw Hill Medical; 2013.
   
2. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, ed. New Delhi: Mc Graw Hill Medical; 2012.
   
3. Bhat S. SRB’s manual of surgery. 3^rd ed. New Delhi: Jaypee Brothers Medical Publishers (P) Ltd; 2009.
   
4. Colon cancer pain [Internet]. 2010 [updated 2010 May 16; cited 2013 July 17]. Available from: https://colon-cancer.emedtv.com/colon-cancer/colon-cancer-pain.html.
   
5. Colon cancer (colorectal cancer [Inyernet]. 1996 [updated 2012 Apr 10; cited 2013 Jul 20]. Avaialble from: https://www.medicinenet.com/colon_cancer/article.htm.
   
6. Colon polyps and cancer [Internet]. 2008 [cited 2013 Apr 20]. Available from: https://gjgastro.com/Education/Colon_Polyps.html.