Colon Cancer
Colon cancer is a common cancer (2nd most common cancer in women and 3rd most common cancer in men), which occurs in the large intestine (colon). The colon (including the rectum) is the last or most distal portion of the digestive tract. Colon cancer normally affects older adults, even though it may affect anyone at any age. Lifetime risk is in the order of 4-5%, and the mean age at diagnosis is 69 years.
Colon cancer typically starts as a polyp (benign tumour or adenoma) which over time (3-8 yrs) becomes cancerous. This "adenoma-carcinoma sequence" provides the rationale for performing screening colonoscopies from the age of 50 years (if no other risk factors present). By removing small benign polyps, the risk of developing cancer in the future can be drastically reduced.
What are the related symptoms of colon cancer?
The signs and symptoms of colorectal cancer depend on the location of the tumour in the colon and whether it has spread elsewhere in the body (metastasis). Tumours in the right side (beginning) of the colon typically give the least symptoms and are usually more advanced at diagnosis. The classic warning signs of colon cancer include:
- Worsening constipation
- Blood in the stool (visible or occult),
- Unexplained iron deficiency anaemia
- Loss of appetite
- Loss of weight and
- Nausea or vomiting in someone over 50 years old.
While rectal bleeding or anaemia are high-risk features in those over the age of 50, other commonly-described symptoms, including weight loss and change in bowel habit, are typically more concerning if associated with bleeding.
In some cases, people who are diagnosed with colon cancer experience no symptoms in early stages and when symptoms do appear, they vary depending on the cancer’s size and location.
When a patient presents with complaints suggestive of colon cancer, Dr Cooper will confirm the diagnosis with some form of imaging. A barium enema (barium is infused into the colon and X-rays are taken to show the inner lining of the colon) or CT colonography can be done, but by far the most common means of diagnosis is to perform a colonoscopy. A colonoscopy has the advantage that it can diagnose the tumour by appearance and also obtain tissue (biopsy) for histological confirmation. It can also diagnose and remove other small polyps, mark the position of the tumour to facilitate laparoscopic surgery and be used to place a stent in a pre-obstructive cancer.
Once the diagnosis has been confirmed, the tumour needs to be staged. Dr Cooper will request a CT scan of the chest and abdomen to check whether there is distant spread (metastases) and to determine if the primary tumour is resectable. If both the above conditions are met, the patient will be evaluated for surgery.
What are the treatment options for colon cancer?
If the patient has prohibitive medical risks (too ill to operate/will not survive the surgery), surgery will not be performed. In all other cases, Dr Cooper may recommend that the patient undergoes a segmental colectomy (removal of the part of the colon that contains cancer as well as the lymph nodes that drain that area of the colon) with primary anastomosis (the ends of the remaining bowel will be re-joined). These procedures can be done in an open or minimally invasive fashion.
Histological evaluation of cancer will determine the need for adjuvant chemotherapy. The aim of chemotherapy will be to prevent the appearance of metastatic disease (systemic spread of cancer) or to treat metastases that are already present. There is good evidence currently that resection of limited/stable liver or lung metastasis can improve the long-term survival in patients with metastatic colon cancer.
The prognosis of colon cancer has improved in recent years due to better chemotherapy agents and earlier detection due to the introduction of screening programs.
Risk factors of colon cancer include diet, obesity, smoking and physical inactivity. Dietary factors that increase the risk of getting colon cancer include high intake of red and processed meat as well as alcohol. Another risk factor is inflammatory bowel disease, which includes Crohn's disease and ulcerative colitis. Some of the inherited conditions that can cause colorectal cancer include familial adenomatous polyposis and hereditary non-polyposis colon cancer; however, these conditions represent less than 5% of cases.