Last updated on 28 January 2021
What is colorectal cancer?
Colorectal cancer is the cancer of the colon (large intestine) and rectum (last 15cm of the large intestine before the anus).
It typically develops very slowly, and most people only experience symptoms when the tumour has reached a significant size. To catch colorectal cancer early, regular screening is recommended as it is possible to detect precancerous changes.
How does colorectal cancer start?
The vast majority of colorectal cancers begin as a growth known as polyps within the colon and rectum.
There are different types of polyps. Some are benign such as hyperplastic polyps and inflammatory polyps, but others can turn cancerous. Polyps that are more likely to turn cancerous are adenomatous polyps, sessile serrated polyps and traditional serrated adenomas.
Regular screening allows doctors to detect them early, when they can be safely and completely removed.
How does colorectal cancer spread?
If cancer is left unchecked, the cancer cells will grow and invade into blood vessels, lymph nodes and nearby organs. Left untreated, these will eventually travel to the other distant organs such as the liver and lungs.
Risk factors for colorectal cancer
Factors that can increase your risks of colorectal cancer include:
- Older age
- Personal history of colorectal cancer or polyps
- Personal history of inflammatory bowel disease such as ulcerative colitis and Crohn’s disease
- Personal history of radiation therapy
- Family history of colorectal cancer
- Inherited syndromes such as familial adenomatous polyposis (FAP) and Lynch syndrome, otherwise known as hereditary nonpolyposis colorectal cancer (HNPCC)
- Alcohol consumption
- Sedentary lifestyle
- Low-fibre, high-fat diet
Symptoms of colorectal cancer
Colorectal cancer is asymptomatic in its early stages. Symptoms of the disease will vary based on how big the tumour is, its location and the stage of the disease.
Signs & symptoms of colorectal cancer include:
- Significant change in your bowel habits
- Bleeding from the anus
- Blood in your stool (bright/dark red or occasionally appearing ‘blackish’)
- Persistent pain in the abdomen
- Loss of appetite
- Persistent lethargy and looking pale or jaundiced
- Unexplained weight loss
Causes of colorectal cancer
There are a few things that may increase your risk for developing colorectal cancer. Some of them can’t be changed, such as increasing age, genetic changes or family history. Other risk factors are often part of the lifestyle you lead, which can be changed or modified. These include smoking, obesity, and being physically inactive.
In addition, a diet that is high in red meat such as beef and processed meats such as ham and bacon are linked to a higher risk for colorectal cancer. Cooking meats at high temperatures such as frying and grilling is also known to create chemical changes in the meat that increase your risk.
Diagnosis of colorectal cancer
After colorectal cancer has been confirmed, further tests to determine the stage of the disease will be ordered by your doctor. This can comprise of blood tests, PET-CT scans, MRI scans, ultrasound scans and further biopsies to obtain tissue samples.
There are different types of blood tests that can be performed. A full blood count (FBC) can reveal if you have anaemia caused by a bleeding tumour. Other blood tests can check for liver enzymes to see if the cancer has spread to the liver, or look for tumour markers that indicate colorectal cancer such as the carcinoembryonic antigen.
In a biopsy, a small piece of tissue from the suspected tumour is extracted and analysed for cancer cells. The sample may be tested for gene changes or, if the cancer has spread (metastasised), checked for specific genes to determine which treatment options might be more effective.
This procedure is the gold standard investigation. It allows your doctor to view the entire length of the colon and rectum, using a colonoscope. This thin, lighted tube with a camera video at the end, is inserted through the anus, passed through the rectum and into the colon. The colonoscope can also allow the use of small instruments to perform biopsies or remove polyps.
A computed tomography (CT) scan uses X-rays to take cross-sectional images, which can show if the cancer has spread to nearby lymph nodes or other organs such as your liver or lungs. In some cases, a CT scan is done with the use of a slightly radioactive substance to highlight cancer cells and make them more visible, known as positron emission tomography (PET).
Magnetic resonance imaging (MRI) scans use radio waves and magnetic fields to take detailed images of soft tissues and organs in the body. It may be done with or without contrast.
Ultrasound uses soundwaves, and the rebounding echo is used to create an image of internal tissues and organs.
Treatment for colorectal cancer
Treatment usually involves surgery to remove the cancer. Other treatments such as chemotherapy and/or radiation therapy may also be recommended. Treatment modalities are individualised for the patient depending on the stage of the cancer, location of the tumour and other health concerns.
Surgery for early stage colorectal cancer
If the tumour is small, a minimally invasive approach to surgery can be performed. This includes:
If the cancer in the polyp is small, it may be possible for your doctor to completely remove the polyp during a colonoscopy.
Endoscopic mucosal resection
For larger polyps, complete removal of the polyp may be performed with a portion of the inner lining of the colon.
Transanal minimally invasive surgery (TAMIS)
This is a specialised minimally invasive surgical approach used to remove large polyps and early cancers within the rectum. It is considered an organ-sparing operation performed entirely through the body’s natural opening (the anus). Unlike traditional surgery, only diseased tissues with clear margins are removed leaving the rest of the normal intestine intact.
Laparoscopic / keyhole surgery
This is a form of minimally invasive surgery, and can be used for tumours that cannot be removed during a colonoscopy. In this operation, your surgeon will make several small incisions in your abdominal wall for the insertion of special cameras and instruments to perform the operation of removing a segment of large intestine together with lymph nodes. As the incisions are smaller, there is less pain, recovery is quicker and there are fewer post-operative complications.
This is another form of minimally invasive surgery that uses small incisions, a camera and surgical instrument. From a surgical console, your surgeon will perform your surgery using various surgical instruments attached to robotic arms. Besides high definition views, the console provides your surgeon with magnified 3D video images, which allow for increased surgical precision. The robotic arms are more ergonomic, with an increased range of motion within a small space, providing greater accuracy which can lead to less surgical trauma, bleeding and post-operative pain.
Surgery for advanced colorectal cancer
In more advanced colorectal cancer cases where the tumour is large, causing blockage or invading into surrounding organs, minimally invasive methods cannot be used. In these cases, open surgery would be required to treat the disease.
A larger incision is made in the abdomen. Your surgeon will use surgical instruments to proceed with the operation to remove the cancer and the involved organs. With a larger incision, the hospital stay will be a few days more compared to minimally invasive surgical approach.
Tumours in the colon and rectum can grow to a size that can cause obstruction to the passage of faeces. Stomas may be required in emergency operations or conditions which preclude with patient from a major surgery such as medical conditions or advanced disease.
A stoma is a surgically created opening in the small or large intestinal which is then brought out to the abdominal wall and stitched to the skin. A bag is attached around the stoma to the abdominal wall for collection of the intestinal contents. The stoma may be temporary to allow for diversion of faecal contents or be permanent in nature.
Screening for colorectal cancer
Did you know that colorectal cancer is the most common cancer in Singapore and is increasingly affecting populations in Asian countries?
Although older adults are more likely to develop this type of cancer, there is an increasing number of adults below the age of 50 being afflicted with this condition.
Removing a polyp can prevent a cancer from occurring. Finding colorectal cancer at its earliest stage through a colonoscopy provides the greatest chance for a cure.
These polyps or early cancers are difficult to detect without proper screening as they do not cause you to exhibit any symptoms when they are small. Hence, for the average risk individual, it is recommended that you go for frequent screening colonoscopy to help detect polyps and cancer early, especially if you are 50 years and older.
To learn more about colorectal cancer or to arrange for a screening, make an appointment with a specialist.
Article reviewed by Dr Jonathan Foo, general surgeon at Mount Elizabeth Hospitals
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