The human colon, or large intestine, is a muscular, tube-shaped organ measuring about 4 feet long.Colon cancer is the most common type of gastrointestinal cancer. It is a multifactorial disease process, with etiology encompassing genetic factors, environmental exposures (including diet), and inflammatory conditions of the digestive tract.
Most colon cancers start in the inner lining of the bowel and develop from small growths called polyps.
Causes and risk factors
We don’t know what causes bowel cancer in most people. There are some risk factors that can increase your chances of getting it.
Age – The risk of developing bowel cancer increases with age.
Diet – A diet containing a lot of red and processed meats and low in fruit and fresh vegetables can increase your risk. Eating fried or grilled meat might also increaseyour risk.
Lifestyle – This includes getting little exercise and being overweight. It also includes smoking heavily and drinking more than the recommended amounts of alcohol overmany years.
Family history – People who have one or more family members with bowel cancer may have a higher risk of developing it. Only about 5% of (5 in every 100) largebowel cancers are thought to be caused by an inherited faulty gene. Talk to yourdoctor if you are worried about your family history.
Familial conditions – Two rare conditions that can run in families, called familial adenomatous polyposis (FAP) and hereditary non-polyposis colon cancer (HNPCC),can increase the risk of developing bowel cancer.
Personal history of inflammatory bowel disease – People who’ve had ulcerative colitis or Crohn’s disease (diseases of the lining of the bowel) for a long time have anincreased risk of developing bowel cancer.
Bowel cancer is not infectious and cannot be passed on to other people.
Symptoms
blood in, or on, the bowel motions – the blood may be bright red or dark in colour
a change in your normal bowel habit (such as diarrhoea or constipation) for no obvious reason, lasting for longer than six weeks
unexplained weight loss
pain in the tummy (abdomen) or back passage
a feeling of not having emptied your bowel properly after a bowel motion
feeling tired and breathless – this can happen if the cancer is bleeding causing anaemia (a low number of red blood cells).
Diagnosis
Laboratory studies that may be helpful include the following:
Complete blood count
Chemistries and liver function tests
Serum carcinoembryonic antigen
Imaging studies that may facilitate staging include the following:
Chest radiography
Chest computed tomography
Abdominal barium study
Abdominal/pelvic CT
Contrast ultrasonography of the abdomen and liver
Abdominal/pelvic MRI
Positron emission tomography, including fusion PET-CT scan
Other procedures that may be warranted include the following:
Colonoscopy
Sigmoidoscopy
Biopsy of suspicious lesions
Double-contrast barium enema
Treatment
Surgery is the only curative modality for localized colon cancer (stage I-III). Surgical resection potentially provides the only curative option for patients with limited metastatic disease in liver and/or lung (stage IV disease). Surgical options include the following:
Right hemicolectomy: For lesions in the cecum and right colon
Extended right hemicolectomy: For lesions in the proximal or middle transverse colon
Left hemicolectomy: For lesions in the splenic flexure and left colon
Sigmoid colectomy: For sigmoid colon lesions
Total abdominal colectomy with ileorectal anastomosis: For selected patients with hereditary nonpolyposis colon cancer, attenuated familial adenomatous polyposis, metachronous cancers in separate colon segments, or acute malignant colon obstructions with unknown status of the proximal bowel
Other therapeutic options for patients who are not surgical candidates include the following:
Cryotherapy
Radiofrequency ablation
Hepatic arterial infusion of chemotherapeutic agents