Specialty Topics

• How does colorectal cancer develop in the body? What happens during colorectal cancer?
  Colorectal cancer develops as a benign or non-cancerous lump in the lining of the colon or rectum. This is called a polyp. There are several types of polyps and the one that commonly leads to cancer is called an adenomatous polyp. Over time, if this polyp is not removed, it undergoes changes to become cancer. The invasive cancer is initially confined in the wall of the colon (often stage I and II) and are curable with surgery. However, if undetected and treated, it spreads to the lymph nodes (stage III) and then to distant organs (stage IV). Cure rates for stage III cancer combining surgery and adjuvant chemotherapy can be as high as 70%. Recent advances in chemotherapy can improve survival, but stage IV disease is usually incurable.
• What are the signs and symptoms? Do patients mistake these signs as the symptoms of another disease?
  Patients with colorectal cancer at an early stage often may not have any signs or symptoms. However, when symptoms do arise, it may be abdominal pain, change in bowel habits, blood in the stools, weakness from blood loss, and weight loss. Using these symptoms to diagnose a person with colorectal cancer can be inaccurate as these symptoms often mimic other non-cancer conditions. In our local experience, the presence of bleeding is often due to piles (haemorrhoids) and brings the patient to the doctor’s attention. However, patient can have piles and colorectal cancer at the same time! Patients with abdominal pain from colorectal cancer can arise from tumour obstruction, blockage or a specific symptom called tenesmus. It means that there is a feeling of incomplete bowel emptying and could mean a tumour in the rectal area.
• Why is colorectal cancer known as a silent killer?
  As mentioned, most patients at an early stage of colorectal cancer do not have symptoms. In addition, colon cancer that develops along the left side of the colon is often more difficult to detect early. This is because the function of the colon is to absorb water from fecal material which gets more formed as it reaches the left side. Hence, the presentation of right sided lesions is often anaemia, or blood loss over time in an occult fashion. For left sided tumours, obstructive symptoms and change of bowel habits predominate.
• Who are at the highest risk?
  Colorectal cancer is rare before the age of 40 years. The incidence rises between the ages of 40 and 50, and the age-specific incidence rates increase in each succeeding decade thereafter. The lifetime incidence of colorectal cancer in patients at average risk is about 5 percent. It is now recognized that there are cohorts of patients and their families at increased risk for colorectal cancer. Some of these uncommon families on our follow up have more than 90% chance of developing colorectal cancer in their lifetime. These patients may have specific inherited conditions that predispose them to develop colorectal cancer. Although some cancer syndromes may have specific physical features, it is often not possible to pick out such individuals. One way to identify at-risk families or individuals is to take a detailed family history which might show multiple kindreds with colorectal or other associated cancers. A discussion with your doctor or a specialist in this area of cancer genetics might be useful. Patients with a inflammatory bowel disease have an elevated risk and recent studies also indicate patients with diabetes mellitus may have an elevated risk compared to non-diabetics.
• What are some of the common prevention methods?
  While epidemiological studies have identified associations with colorectal cancer, some of the associations are not particularly strong and may be difficult to interpret. Several studies have shown that increased alcohol intake may affect folate metabolism and intake resulting in a modest increase in colorectal cancer risk. Obesity measured by an increased body mass index has been associated with an elevated colorectal cancer risk in two studies. Reducing alcohol intake and obesity are good starting measures to reduce the risk for colorectal cancer.
  
  Many studies have shown an association between the intake of a diet high in fruits and vegetables and protection from colorectal cancer. However, the protective effect could be due to the fiber, antioxidant vitamins, folic acid, minerals such as selenium, other micronutrients, or phytochemicals (flavones) in vegetables or is due to a combined effect, or to some other constituent(s) is not known. In addition, other studies such as the Nurses’ Health Study and the Health Professionals' Follow-up Study have not shown a relationship between consumption of fruits, vegetables and colorectal cancer risk. Given that such studies are difficult to conduct, it is not surprising to have discordant findings.
  
  Taking aspirin and the group of medication called NSAIDS to reduce the risk for colorectal cancer has been explored. The current thinking is that it is useful in above average risk individuals from high risk colorectal cancer families. This is because taking such medications over prolonged periods of time entails other risks of the medication include haemorrhage and other health problems. On an individual basis because of familial risk, an appropriate discussion with a doctor should be carried out.
• What are the treatment methods, and which are most often used? - Please include a small segment on KRAS biomarker and KRAS testing on diagnosis.
  The treatment of colon cancer usually involves surgery, and it may also involve chemotherapy and radiation therapy. Surgery is the most common initial modality used for colon cancer. During the surgery, the cancerous part of the colon and surrounding tissues are removed. Lymph nodes are also removed to examined if they have been affected by the cancer. In some people, the two ends of the colon can be joined immediately but some patients may require a colostomy. This can be temporary for some patients but some may require this permanently.
  
  Chemotherapy is a treatment given to slow or stop the growth of cancer cells. After surgery, in some patients, cancer cells can remain in the body, increasing the chance of a recurrence. Chemotherapy given after surgery is called “adjuvant”, and increases the chance of a cure. The chemotherapy usually lasts 6 to 8 months and involves a combination of drugs. Most chemotherapy are given as intravenous injections but there are some are oral medications. In addition, chemotherapy is sometimes combined with radiation therapy particularly in rectal cancer before surgery to shrink the tumour so that the chance that the tumour comes back is less and avoiding a colostomy for some patients.
  
  In advanced cancer, chemotherapy is the primary modality of treatment. Newer medications exploiting the signaling and other pathways of cancer development has led to new drugs development which in many cases have fewer of the side effects traditionally associated with chemotherapy such as hair loss or low blood counts. An example is a monoclonal antibody directed against the epidermal growth factor receptor. In combination with chemotherapy, this drug has been shown to improve survival in advanced colorectal cancer patients but only in those with a genetic marker called Kras that is normal (wild type) in the tumour. Such advances allow doctors to identify by testing for the mutation status of the gene in the tumour to see which patients benefit.
• What are the screening methods?
  Colorectal cancer often bleeds and the microscopic blood or abnormal DNA markers can be detected. Locally, the microscopic occult blood test is the test widely available. If occult blood is detected in the stools, a person needs to have an examination of the colon by endoscopy. It does not mean that when there is occult blood that cancer is always present. Many factors can create a test that is positive such as gastric ulcers, diet, some medications such as aspirin. In addition, polyps and early cancers may not bleed often enough to be detected. The test is not suitable for individuals who already have bleeding piles. It has to be done yearly for screening to be effective.
  
  Colonoscopy or sigmoidoscopy are techniques that allow the examination of the lining of the large bowel wall. During colonoscopy, under sedation, a thin, lighted tube is used to directly view the lining of the rectum and the entire colon. Polyps can be removed during this procedure. The preparation for the procedure means that a person has to cleanse the bowel by taking a liquid medication the night before.
  
  Some people may have heard of CT colonography which is using a CT scan to take X-ray images of the colon with computer reconstruction. Traditional bowel preparation is still needed and if a polyp were to be detected, a colonoscopy would still be needed to remove it. A double contrast barium enema is procedure to image the large bowel using barium contrast administered as an enema. It is not used as much nowadays.
  
  Screening for average risk individuals is from 50 years onwards but there are many people at elevated risk whereby screening has to start earlier and sometimes may be more frequent. In addition, some at risk families may be better screened with colonoscopy because they tend to develop cancer at the right (proximal) side of the colon.
• Why do people put off screening?
  There are different and complex reasons why people put off screening. Inertia or just feeling that “it will not happen to me” is common. Screening requires that extra effort to take time or maybe leave off work to have a test done. However, colorectal cancer is now the most common cancer in this country especially affecting the above 50 year old age group, so the time taken to do the test is well invested. In Singapore, these tests are readily available from one’s family physician or doctor and the quality of testing is good. In colorectal cancer, the removal of the polyp as explained would in fact save a lot more effort and time later on if a person were to be found to have invasive colorectal cancer instead.
  
  People fear knowing one’s own cancer diagnosis. I think it is important for us to emphasize to the public that colorectal cancer is curable when detected early. In particular, colorectal cancer has been clearly worked out as a model for carcinogenesis by Vogelstein and Fearon. This means that there is a progression from adenoma (polyp) to carcinoma and the opportunity to interrupt that progression by screening and removal of the polyp. If a person understands that the screening for colorectal cancer is really looking for precancerous polyps which will lead to a cure when removed, this is even better than detecting the cancer.
  
  In this era of health care costs being a prominent issue, cost of testing and follow up is important. Some people may also feel uncomfortable with a screening endoscope from the bottom end. For colorectal cancer, there are several modalities of screening and choices. Screening for average risk individuals with stool occult blood has to be done yearly whereas if a person with a normal colonoscopy would not have to repeat it for 10 years.
• What are the survival rates at the different stages? Can the cancer be nipped in the bud if caught early?
  The 5 year survival rate is highest when colorectal cancer is diagnosed early. In fact, some of our patients have had polyps removed with early cancer that has not even invaded the wall of the colon. In general, the 5 year survival for stage I colorectal rectal cancer is more than 90%, it is about 70 to 80% for stage II. There is a drop to about 40 to 65% for stage III. Some stage IV patients do survive 5 years, although it is a minority at about 8%.
• Do you observe colorectal cancer being on the rise?
  Yes, the incidence of colorectal cancer is on the rise. It is not only in Singapore but also in many other developed countries. Regionally, many of Asian countries like Japan, China, and South Korea are also experiencing an increased incidence. The rising trend in incidence and mortality seems to affect more affluent societies. However, the underlying causes ascribed to dietary habits and lifestyle are complex. Certainly, it pays to remember that it is becoming a common disease in the above 50 year old population. Efforts should be made to detect it early and to improve the care and cure of patients.