Colorectal cancer is a cancer that starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.
Cancer starts when cells in the body start to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. Doctors have concluded that the increasing consumption of fast food, which is low in fibre, may be a key contributing factor. In India, colon and rectal cancers are seen in relatively young patients, as compared to the western population.
Adenocarcinomas make up about 96% of colorectal cancers. These cancers start in cells that make mucus to lubricate the inside of the colon and rectum. When doctors talk about colorectal cancer, they're almost always talking about this type. Some sub-types of adenocarcinoma, such as signet ring and mucinous, may have a unfavourable prognosis (outlook).
Other, much less common types of tumours can start in the colon and rectum, too:
- Carcinoid tumours: These start from special hormone-making cells in the intestine. Click Here to read more about carcinoid tumours
- Gastrointestinal stromal tumours (GISTs): start from special cells in the wall of the colon called the interstitial cells of Cajal. Some are not cancer (benign). These tumours can be found anywhere in the digestive tract, but are not common in the colon.
- Lymphomas are cancers of immune system cells. They mostly start in lymph nodes, but they can also start in the colon, rectum, or other organs. Click here to know more about Non-Hodgkin Lymphoma.
- Sarcomas can start in blood vessels, muscle layers, or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare. Click here to know more about Soft Tissue Sarcoma.
In its early stage, colorectal cancer usually doesn’t have symptoms. It is therefore important to keep up with the tests the doctor recommends for an early detection and correct diagnosis. However, when symptoms do appear, the following are most likely:
- A change in your bowel habits, including diarrhoea or a change in the consistency of stool for more than a couple of weeks
- Rectal bleeding or blood in stool
- Persistent abdominal discomfort, such as cramps, gas or pain
- Abdominal pain with bowel movement
- A feeling that the bowel doesn't empty completely
- Unexplained weight loss and fatigue
Anyone can get colorectal cancer, and doctors often don't know why someone gets it. Although scientists don’t know the exact cause, they do know some of the things that make people more likely to get it. These include:
- Age: The disease is most common in people over age 50, and the chance of getting colorectal cancer increases with each decade.
- Gender: Colorectal cancer is more common among men. Men and women are equally at risk for colon cancer, but men are more likely to develop rectal cancer.
- Polyps: These growths on the inner wall of the colon or rectum aren’t cancer, but they can be precancerous. Polyps are fairly common in people over age 50. One type of polyp, called an adenoma, makes colorectal cancer more likely. Adenomas are the first step toward colon and rectal cancer.
- Personal history: If you’ve already had colorectal cancer, you could get it again, especially if you had it for the first time before age 60. Also, people who have chronic inflammatory conditions of the colon, such as ulcerative colitis or Crohn's disease, are more likely to develop colorectal cancer
- Family history: If a family member has had colorectal cancer it makes one more likely to get it, too. If that relative was diagnosed when he or she was younger than 45 years old, the risk is even higher. If conditions such as familial adenomatous polyposis, MYH-associated polyposis, or hereditary non-polyposis colorectal cancer run in the family, that raises the risk for colon cancer.
- Diet: People who eat a lot of fat and cholesterol and little fibre may be more likely to develop colorectal cancer.
- Lifestyle: It is more likely to get colorectal cancer if one drinks a lot of alcohol, smokes, doesn’t get enough exercise, and if they are overweight.
- Diabetes: People with diabetes are more likely to develop colorectal cancer than other people.
People with the following risks should begin colon screening before age 45:
- Family history of inflammatory bowel disease, other colorectal diseases, polyps or familial adenomatous polyposis
- People with a family history of hereditary nonpolyposis colon cancer
The diagnosis of colorectal cancer is done through the below tests:
- Stool Based tests:
- Faecal immunochemical test (FIT) yearly
- Guaiac faecal occult blood test yearly
- Stool DNA test every 3 years
- Structural Examinations:
- Colonoscopy every 10 years
- Flexible sigmoidoscopy every 5 years
- CT colonography (virtual colonoscopy) every 5 years.
Any suspicious symptoms or abnormalities will alert your doctor to perform a colonoscopy to get a biopsy. Should a biopsy confirm cancer, imaging tests using chest X-rays and CT scans of the abdomen, pelvis, and possibly chest are performed to find out whether the cancer has spread to other sites.
Blood tests will also be ordered to find out how well the liver and kidneys are functioning, to determine if you are anaemic, and to measure the blood level of a substance called carcinoembryonic antigen (CEA), often found in higher-than-normal concentration in the presence of colorectal cancer, especially if it has spread.
The main types of treatment for colorectal cancer are surgery, radiation therapy, chemotherapy, targeted therapy, and immunotherapy. Depending on the cancer stage, these treatments may be combined for a better outcome.
- Surgery is the most effective treatment for localised colorectal tumours. Very small tumours can be removed through a colonoscope, but even with small tumours, removing the portion of the colon containing the tumour, the surrounding fat, and nearby lymph nodes is often the best treatment. Surgery may be performed either laparoscopically or by the open method, which uses larger incisions. Usually, the healthy sections of the colon and rectum gets reconnected. In cases where this is not possible, an opening is formed, known as a stoma, in the abdomen and the severed colon is rerouted to it. Waste matter is collected in a bag worn over the stoma. This is known as a colostomy and is often only temporary. Once the bowel has had time to heal, a second operation is done to reconnect the colon and rectum. The need for permanent colostomy is more common with rectal cancer, since retaining the rectum may be difficult.
- Radiation therapy is treatment with high-energy rays that destroy the cancer cells. For rectal cancer, radiation is usually given after surgery, along with chemotherapy (known as adjuvant therapy) to destroy any cancer cells left behind. It can also be used along with chemotherapy before surgery (known as neoadjuvant therapy) in order to shrink the size of the tumour, making the surgery easier. In advanced rectal cancer, radiation can be used to shrink tumours that cause symptoms of bowel obstruction, bleeding, or pain.
- Chemotherapy is used to treat various stages of colorectal cancer, especially the advanced stages where metastasis has happened. If the cancer has metastasized to the liver chemotherapy can also be directly administered there.
- Targeted therapy works in a completely different way in treating colorectal cancer. Through this treatment, the aim is to block the cancer’s blood supply or block a protein or genetic change made by the cancer to enhance it growth. This form of treatment is effective especially after metastasis
- Immunotherapy involves drugs that stimulate the body’s own immune system to recognize and destroy cancer cells.