Colorectal cancer, also known as colon cancer, rectal cancer, or bowel cancer, is any cancer which affects the rectum and the colon. The rectum and colon are parts of the large intestine. The colon is a U-shaped tube made of muscle which is found below the stomach. Whereas, the rectum is a shorter tube connected to the colon.
In India, colorectal cancer is the third leading cause of cancer death in women, and the fourth for men. However, with advancement in screening techniques and improvement in treatments, the death rate from this disease has been falling.
Types of colorectal cancer
There is actually more than one type of colorectal cancer. The differences have to do with the types of cells that become cancerous as well as where they grow.
Adenocarcinomas make up for the most common type of colon cancer. They make up 96 per cent of all the cases. Unless the doctor specifies otherwise, the colon cancer is likely this type. Adenocarcinomas begin within the mucus cells in either the rectum or colon.
Less commonly, colorectal cancers are a result from other types of tumors, like:
- Carcinoids, which form in the hormone-making cells within the intestines
- Sarcomas, which form in the soft tissues like muscles in the colon
- Lymphomas, which can form in lymph nodes or in the colon first
- Gastrointestinal stromal tumors, which can begin as benign and then become cancerous. These usually begin in the digestive tract, but rarely in the colon.
Some of the symptoms of colorectal cancer are:
- Diarrhea or constipation
- Changes in bowel habits
- Blood in feces that makes stools look black
- A feeling that the bowel does not empty properly after a movement
- Bright red blood coming from the rectum
- Bloating and pain in the abdomen
- Fatigue or tiredness
- A feeling of fullness in the abdomen, even after not eating for a long time
- Unexplained weight loss
- A lump in the back passage or abdomen felt by the doctor
- Unexplained iron deficiency in men or in women after menopause
An important point to note is that most of these symptoms may also indicate other possible problems. It is important to see a doctor if these signs persist for four weeks or more.
Causes and diagnosis
Doctors are not certain what exactly causes colon cancers. In general, it begins when healthy cells in the colon develop changes in their DNA. A cell’s DNA has a set of instructions that tell a cell what to do.
Healthy cells grow and divide in a definite way to keep the body functioning normally. But when a cell’s DNA is damaged and becomes cancerous, cells continue to divide, even when they are not needed. As the cells accumulate, they form a mass.
With time, the cancer cells can grow to spread and kill normal tissue nearby. And cancerous cells can travel elsewhere in the body to form deposits.
The following are the most common diagnostic procedures for colorectal cancer:
- Fecal occult blood test or blood stool test – This test involves taking a sample of the patient’s stool for the presence of blood. It can be done at the doctor’s office or with a kit at home. A blood stool test is not fully accurate because not all cancers cause a loss of blood or bleeding all the time. Hence, this test can give a false negative result.
- Flexible sigmoidoscopy – The doctor uses a sigmoidoscope which is a slender, flexible and lighted tube to examine the patient’s sigmoid and rectum. The sigmoid colon is the last part of the large bowel before the rectum.
If a doctor detects polyps or colon cancer, a colonoscopy can be used to examine the entire colon and take out any polyps that are located. These will be analyzed under a microscope.
A sigmoidoscopy will only detect polyps or cancer in the end third of the rectum and the colon. It will not detect an issue in any other part of the digestive tract.
- Stool DNA test – This test analyzes several DNA markers that precancerous polyps or colon cancer cells shed into the stool. This test is more accurate for detecting colon cancer than polyps, but it cannot detect all DNA mutations that indicate that a tumor is present.
- Barium enema X-ray – Barium is a contrast dye that is placed into the person’s bowel in an enema form, and it comes up on an x-ray. In a double-contrast barium enema, air is also added.
The barium fills and coats the lining of the bowel, creating an image of the colon, rectum, and occasionally a small part of the person’s small intestine.
A flexible sigmoidoscopy may be done to detect small polyps the barium enema X-ray may miss. If the x-ray detects anything unusual, the doctor may recommend a colonoscopy.
- Colonoscopy – A colonoscope is longer than a sigmoidoscope. It is a flexible, long, and slender tube, attached to a monitor and video camera. The doctor can see the whole rectum and colon. Any polyps identified during this examination can be removed during the procedure, and sometimes biopsies, or tissue samples are taken instead.
- CT colonography – A CT machine takes images of the colon, after clearing it. If anything unusual is detected, conventional colonoscopy may be necessary. This procedure may offer patients an alternative to colonoscopy that is better-tolerated, less-invasive, and with good diagnostic accuracy.
Stages and treatment options
The stages of colorectal cancer are:
- Stage 0 – This is the earliest stage, when the cancer is still within the inner layer, or mucosa of the rectum or colon. It is also known as carcinoma in situ.
- Stage 1 – The cancer has grown through the inner layer of the rectum or colon but has not spread beyond their wall.
- Stage 2 – The cancer has grown through or into the wall of the rectum or colon, however it has not yet reached the nearby lymph nodes.
- Stage 3 – The cancer has reached the nearby lymph nodes, but it has not yet affected other parts of the body.
- Stage 4 – The cancer has spread to other parts of the body, including other organs, such as the lung, liver, the membrane lining the abdominal cavity, or the ovaries.
Treatment for colorectal cancer will depend on several factors, including the location, size, and stage of the cancer, whether or not it is recurrent, and personal preference.
- Surgery – This is the most commonly done treatment. The affected malignant tumors and nearby lymph nodes will be removed to reduce the risk of the cancer spreading.
The bowel is usually sewn back together, however sometimes the rectum is removed completely and instead a colostomy bag is attached for drainage. The bag collects stools. It is usually a temporary setting, but it may be permanent if it is not possible to join up the ends of the bowel.
- Chemotherapy – Chemotherapy involves using a chemical or medicine to destroy the cancerous cells. Before surgery, it may help shrink the tumor.
Targeted therapy is a kind of chemotherapy that specifically targets the proteins that encourage the growth of some cancers.
- Radiation therapy – It uses high energy radiation beams to kill the cancer cells and to prevent them from growing. This is more commonly used for treating rectal cancer.
- Ablation – It can destroy a tumor without removing it. Ablation can be done using ethanol, radiofrequency, or cryosurgery. These are delivered using a needle or probe that is directed by ultrasound or CT scanning technology.
Side effects of treatment
Treating colon cancer can save your life. But, treatment is not without side effects. Some of these include:
- Hair loss
- Mouth sores, nausea and vomiting
- Nerve damage (neuropathy)
- Bleeding or bruising easily
Survivorship and prevention for colorectal cancer
Once you have completed the treatment, you will need to meet with your health care team to review the treatment summary and form a surveillance plan. The treatment summary is a list of all the treatments you have received, including when it occurred.
The surveillance care plan helps the team look after you closely for cancer recurrence in the months and years after treatment. The doctor will schedule clinic visits and recommend screening tests at specific time periods. While the follow-up schedule will differ from individual to individual, it usually includes:
- Physical exams
- Computed tomography (CT) and other imaging tests
- Blood work to check for tumor markers
Certain lifestyle measures may reduce the risk of developing colorectal cancer:
- Nutrition – Follow a diet with plenty of fiber, vegetables, fruits, and good quality carbohydrates and a minimum of processed and red meats. Switch from saturated fats to good quality fats, such as olive oil, avocado, nuts and fish oils.
- Regular screenings – People who are over 50 years of age, who have had colorectal cancer before, who have a family history of this type of cancer, or who have Lynch syndrome, Crohn’s disease, or adenomatous polyposis should have regular screenings.
- Exercise – Moderate, regular exercise has been proven to have a significant impact on lowering a person’s risk of having colorectal cancer.
- Bodyweight – Being obese or overweight raises the risk of various cancers, including colorectal cancer.
In addition to living a healthier lifestyle, it is important to follow the doctor’s recommendations on screening and follow-up visits. Proper care will ensure that you get the best treatment possible in the event that the cancer returns.