The colon and rectum together form the large intestine. It is the last part of the digestive system. It begins where
the small intestine ends at the right lower corner of the abdomen. It travels upwards towards the liver at the right
upper quadrant, then turns and goes across the abdomen to the left upper quadrant. From there, it turns downwards
and travels to the left lower part of the abdomen.
It then travels towards the centre of the pelvis and goes straight down and ends at the anus. The rectum forms the last 15cm of the large intestines and lies within the pelvis. It is so named because it is relatively straight.
Cancer is an abnormal growth of cells that has the ability to invade into surrounding organs as well as spread to distant sites.
Colorectal cancer originates from the inner lining or mucosa of the colon and rectum. The lining of the colon is
continuously growing and shedding. As such, the lining or mucosa is undergoing cell replication all the times. With each
replication, there is always a chance of a mutation. Although most mutations are recognised as an error by the body and
the mutant cell is removed, sometimes these mutant cells escape the body's defence mechanism and continue to grow. As
they grow, more mutation may occur and after a sequence of 4 or 5 mutations in the cell, they may turn cancerous.
Most of the colon cancer follows the adenoma-carcinoma sequence. What this means is that the colon wall first mutates into adenoma (a non-cancerous form) and over time with more mutation, changes into carcinoma (cancer).
The adenoma is usually in the form of a polyp which is a fleshy protuberance from the colon wall. Larger polyps may appear to have a stalk due to the weight of the polyp pulling on the colon lining.
With time, the adenoma type tissue in the polyp will turn cancerous. It then invades back into the polyp and up the stalk (if there is one) and eventually into the wall of the colon.
Once colon cancer has invaded into the wall, it can then spread to distant organs either via the blood stream or the lymphatic system.
To know more about colorectal cancer, contact Ho Kok Sun Colorectal today at 6737 2778. You can also schedule an appointment with our colon surgeon, Dr Ho Kok Sun, for enquiries regarding our colorectal cancer screening options.
Staging is a way to measure the spread of a cancer. The later the stage, the greater the risk of recurrence of the
cancer. This gives your doctor a way to predict your risks and to advise if further treatment is required.
Most treatments are based on the TNM system. T is for tumour, and it is giving a number of 1 to 4 depending on the depth of invasion of the tumour at the wall of the colon or rectum. N is nodal status and is given based on the number of affected lymph nodes around the region. N0 is given when none of the surrounding lymph nodes are affected.
The greater the number of affected nodes, the larger the N number (0,1 or 2). M stands for metastasis. This means that the cancer has spread to distant organs. M0 means no metastasis and M1 means it has spread. M1 almost always equates to a stage 4 cancer. Various combinations of the T, N and M stage will give the actual stage of the disease.
|AJCC Stage||TNM stage||TNM stage criteria for colorectal cancer|
|Stage I||T1 N0 M0||T1: Tumor invades submucosa|
|Stage I||T2 N0 M0||T2: Tumor invades muscularis propria|
|Stage II-A||T3 N0 M0||T3: Tumor invades subserosa or beyond (without other organs involved)|
|Stage II-B||T4 N0 M0||T4: Tumor invades adjacent organs or perforates the visceral peritoneum|
|Stage III-A||T1-2 N1 M0||N1: Metastasis to 1 to 3 regional lymph nodes. T1 or T2.|
|Stage III-B||T3-4 N1 M0||N1: Metastasis to 1 to 3 regional lymph nodes. T3 or T4.|
|Stage III-C||any T, N2 M0||N2: Metastasis to 4 or more regional lymph nodes. Any T.|
|Stage IV||any T, any N, M1||M1: Distant metastases present . Any T , any N.|
Cancer staging is accurate only after removal of the cancer. It is not possible to tell the stage of a cancer at the
time of colonoscopy. This is because a colonoscopy only allows
your doctor to see the inside of your colon and will not be able to see the lymph nodes nor other organs such as the
liver or lung.
CT scans will be able to tell if there is or is not metastasis (the M stage). It is not sensitive enough to tell the status of the lymph nodes. Hence, if there is no spread to the liver or lung in the scan, the only conclusion that can be drawn is that it is not a stage 4 cancer.
It is important to note that polyps, even large ones, and early cancer may not have any symptoms at all. Symptoms also
depend on the site of the cancer and how far away it is from the end of the colon. When stools enter the colon from the
small intestines, it is in a semi-solid state. As it stays and travels along the colon, the water in it gets absorbed by
the colon and it becomes more solid.
As such, tumour in the right side of the colon do not usually cause much symptoms as the semi-solid stools can flow past most tumours quite easily. The cancer may bleed silently as it is mixed in the stools and cannot be seen with the naked eye. Patients with tumours here usually present late with symptoms of anemia (low blood levels). Symptoms of anemia include tiredness, feeling breathless when walking the same distance or climbing stairs, frequent giddiness.
At the left side of the colon, the stools are more solid. Therefore, any narrowing of the colon lumen results in the following disturbance of the bowel habit:
For tumours in the rectum, the patient may have the sensation of incomplete passage of stools. This is because the
presence of the tumour there imitates the presence of stools.
Other less specific symptoms include feeling of bloating and mucus in the stools. Pain is usually not a feature of colon and rectum cancer until it is at an advanced stage. One complication of the tumour is intestinal obstruction. This means that the entire passageway is blocked and the stools (and even flatus) are not able to pass through. This results in abdominal pain, distension and at a later stage, vomiting. Intestinal obstruction is an emergency medical condition.
Physical examination usually does not yield much signs unless the cancer is in an advanced stage. A hard mass in the abdomen is usually a sign of a large tumour. An enlarged liver signifies spread of the cancer to the liver. In some rectal cancers, a digital rectal examination where your colorectal doctor inserts a finger up the anus may pick up earlier cancers. As such, if your colorectal doctor thinks that you warrant a rectal examination, please do not decline or refuse for fear of discomfort or embarrassment.
All the different tests to examine the colon requires proper cleansing of the colon. There are 3 different ways to examine the colon: colonoscopy, barium enema and computer tomography (CT) colonography (also known as virtual colonoscopy).
|Colonoscopy||Barium enema||CT colonography|
|Advantages||Accuracy- highest, especially for smaller polyps||Lower perforation risk||Lower perforation risk|
|Disadvantages||Perceived invasive test Perforation risk 0.1%||Least accurate |
Perforation risk 0.04%
|Accuracy in between barium enema and colonoscopy. Detection for polyps drop when size below 10mm Perforation risk 0.05 %|
|Sedation||Available||Not available||Not available|
|Intervention||Allows biopsy and removal of polyp||No||No|
Surgery is the only treatment that a colorectal surgeon can offer for the definite cure of colon and
rectum cancer. Other treatment modalities such as chemotherapy and radiation therapy may be used as additional
treatment in reducing the risk of recurrence but do not consistently offer a cure.
The principle behind surgery for colon and rectum cancer is to remove the segment of colon or rectum with the cancer together with the adjacent area containing the lymph nodes where the cancer would initially spread. After the segment of the colon or rectum with the cancer is removed, the intestines are joined back to restore continuity so that the patient can continue to pass motion in the normal manner.
In cases where the tumour is very close to or invading the anus, the anus would have to be removed to ensure that the cancer is completely excised.
In certain cases of rectal cancer, the colorectal surgeon may also decide to pull out a temporary stoma. This is because the joint (anastomosis) for the colon to anus has a higher rate of non-healing. Having the temporary stoma acts to divert stools away from the anastomosis so that even if it does not heal properly, there would not be any leakage of stools into the abdominal cavity and cause major complication and infection. In these cases of temporary stoma, the stoma will be closed about 6 weeks to 3 months later.