Colorectal cancer, commonly known as colon cancer or bowel cancer, originates from the tissues of the colon (the longest part of the large intestine) or rectum (the last several inches of the large intestine before the anus). Most colorectal cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).
It is the most common cancer in Singapore. The incidence of this cancer has been steadily increasing in both males and females. Singapore has one of the highest incidence of this cancer in Asia together with Taiwan, Japan and Australia. The good news is that the number of deaths from colorectal cancer has been dropping for the last 15 years. This is because more people are going for regular screening, which can detect colorectal cancers early. Treatment for colorectal cancer has also improved, allowing for patients to be treated more effectively. Early detection of colorectal cancer can normally lead to a complete cure.
There is no single cause of colorectal cancer, as in most cases, colon cancers begin as a polyp that develops into a cancerous growth.
Anatomy of the Colon and Rectum
What Causes Colorectal Cancer?
No one knows the exact causes of colorectal cancer. However, we do know that people with certain risk factors are more likely than others to develop colorectal cancer. Studies have found the following risk factors for colorectal cancer:
Polyps are growths on the inner wall of the colon or rectum and is common in people over age 50. Most polyps are benign (not cancer), but some polyps (adenomas) can become cancer.
Ulcerative colitis or Crohn’s disease
A person who has had a condition that causes inflammation of the colon (such as ulcerative colitis or Crohn’s disease) for many years is at an increased risk.
Personal history of cancer
A person who has already had colorectal cancer may develop colorectal cancer a second time. Also, women with a history of cancer of the ovary, uterus (endometrium), or breast are at a somewhat higher risk of developing colorectal cancer.
Family history of colorectal cancer
If you have a positive family history of colorectal cancer, you are more likely than others to develop this disease, especially if your relative had the cancer at a young age.
Individuals who smoke, or consume a diet that is high in fat and low in fruits and vegetables are at an increased risk of colorectal cancer.
Age over 50
Colorectal cancer is more likely to occur as people get older. More than 90 percent of people with this disease are diagnosed after age 50 years and above.
Signs and Symptoms
Warning Signs of Colorectal Cancer
A common symptom of colorectal cancer is a change in bowel habits. Symptoms include:
- Change in bowel habits (diarrhea or constipation)
- Feeling that your bowel does not empty completely
- Finding blood (either bright red or very dark) in your stool
- Finding your stools are narrower than usual
- Frequently having gas pains or cramps, or feeling full or bloated
- Losing weight with no known reason
- Feeling very tired all the time
- Having nausea or vomiting
Most often, these symptoms are not due to cancer. Other health problems can cause some of these symptoms. Additionally, it is important to note that early cancer does not usually cause pain. Therefore, anyone with these symptoms should see a doctor to be diagnosed and treated as early as possible.
Screening tests help your doctor find polyps or cancer before you have symptoms. Early detection of colorectal cancer will also improve effectiveness of cancer treatment. The following screening tests can be used to detect polyps, cancer, or other abnormalities.
Fecal Occult Blood Test (FOBT)
Sometimes cancers or polyps bleed, and the FOBT can detect tiny amounts of blood in the stool. If this test detects blood, other tests are needed to find the source of the blood. Benign conditions (such as hemorrhoids), can also cause blood in the stool.
Your doctor examines your rectum and the lower part of the colon with a lighted tube (sigmoidoscpe). If polyps (benign growths that may lead to cancer) are found, they may be removed.
Your doctor examines your rectum and entire colon using a long, lighted tube (colonoscope). If polyps (benign growths that may lead to cancer) are found, they may be removed.
Double-contrast barium enema
This procedure involves filling the colon and rectum with a white liquid material (barium) to enhance x-ray pictures. Abnormalities (such as polyps) can be seen clearly.
In this test, special X-ray equipment is used to produce pictures of the colon and rectum. A computer assembles these pictures into detailed images that can show polyps and other abnormalities.
Diagnosis & Assessment
If you have a symptom or screening result that suggests colorectal cancer, your doctor must find out whether it originates from cancer or other health conditions.
Your doctor will ask about your personal and family medical history and perform a physical examination.
If abnormalities (such as polyps) are found, a biopsy may be required. Often, the abnormal tissue can be removed during colonoscopy or sigmoidoscopy. A pathologist checks the tissue for cancer cells using a microscope.
How is Colorectal Cancer Assessed?
If the biopsy shows that cancer is present, your doctor needs to know the extent of the disease to plan the best treatment. The stage is based on whether the tumor has invaded nearby tissues, whether the cancer has spread and, if so, to what parts of the body.
Doctors describe colorectal cancer by the following stages:
- Stage 0: The cancer is found only in the innermost lining of the colon or rectum. Carcinoma in situ is another name for Stage 0 colorectal cancer.
- Stage I: The tumor has grown into the inner wall of the colon or rectum. The tumor has not grown through the wall.
- Stage II: The tumor extends more deeply into or through the wall of the colon or rectum. It may have invaded nearby tissue, but cancer cells have not spread to the lymph nodes.
- Stage III: The cancer has spread to nearby lymph nodes, but not to other parts of the body.
- Stage IV: The cancer has spread to other parts of the body, such as the liver or lungs.
- Recurrence: This is cancer that has been treated and has returned after a period of time when the cancer could not be detected. The disease may return in the colon or rectum, or in another part of the body.
Treatment & Care
Surgery involves the removal of tissues that contain the tumor and nearby tissues/lymph nodes. This may be done via laparoscopy or open surgery.
Chemotherapy uses anticancer drugs to shrink/kill cancer cells. The drugs enter the bloodstream and can affect cancer cells all over the body.
Targeted Cancer Therapy
Some people with colorectal cancer that has spread receive targeted therapy. Targeted therapies are drugs or other substances that block the growth and spread of cancer by interfering with specific molecules involved in tumor growth and spread.
Radiation therapy (also called radiotherapy) uses high-energy rays to kill cancer cells. It affects cancer cells only in the treated area.
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