Colorectal cancer is any tumor that begins in the rectum or the colon. The cancers are named rectal cancer or colon cancer depending on where they begin, but are grouped under one name because they share common features. The rectum and colon are parts of the large intestine, the lower part of the digestive system. Food usually goes through the stomach then into the small intestine before reaching the colon. In the colon, water and essential nutrients are absorbed from food while waste matter (stool) is stored. From the colon, stool moves into the rectum before leaving the body.
How does colorectal cancer start?
Colorectal cancer begins when cells of the rectum or colon grow out of control. Usually, this occurs when cells of the inner lining of the rectum or colon form clumps or growths called polyps. Generally, polyps are small, noncancerous clumps of cells, which produce few or no symptoms. But over time, some polyps may change and become cancerous. The risk of polyps becoming cancerous depends on the type, size and number of polyps. For example, adenomatous polyps or dysplasia in the colon or rectum may result in cancer (they are pre-cancerous) while inflammatory and hyperplastic polyps do not lead to colorectal cancer. Once cancer begins in a polyp, it spreads into the wall of the rectum or colon. For this reason, regular screening tests are recommended as a way of identifying and removing polyps before colorectal cancer develops.
Types of colorectal cancer
1. Adenocarcinomas: Colorectal cancers that begin in the mucus cells of the rectum and colon. They make up 95 percent of all colorectal cancers.
2. Carcinoid tumors: Tumors that begin in specialized hormone-producing cells of the large intestines.
3. Lymphomas: Cancers of immune system cells that oten begin in the lymph nodes, but occasionally start in the rectum or colon.
4. Gastrointestinal stromal tumors (GISTs): Tumors that begin in the specialized cells called interstitial cells of Cajal, which are found in the wall of the colon. Some are non-cancerous while others are cancerous.
5. Sarcomas: Rare cancers of the rectum and colon which start in the muscle layers, blood vessels or other connective tissues of the rectal or colon wall.
How common is colorectal cancer?
In the United States, colorectal cancer is the fourth most common cancer diagnosed, with more than 95,000 new cases of colon cancer and more than 40,000 new cases of rectal cancer reported annually. The cancer occurs equally in men and women, but men usually develop it at a younger age. About 1 in every 20 people in the United States will have colorectal cancer in their lifetime, with men having a slightly higher risk than women. Colorectal cancer is the second-leading cause of cancer-related deaths in men and third-leading cause in women in the U.S. It currently causes more than 50,000 deaths annually. However, over the last few decades, the death rate due to colorectal cancer has reduced significantly as early screening, detection and treatment has ensured increased survival. Today, there are more than 1 million colorectal cancer survivors in the United States.
Causes of colorectal cancer
In most cases, the causes of colorectal cancer are unclear. Nevertheless, a number of risk factors have been recognized over the years. A risk factor is anything that may increase the chances of developing colon or rectal cancer. The risk factors include:
1. Age: Over 90 percent of colorectal cancer cases are found in people 50 years or older. However, the cancer may still occur at any age.
2. Family history: If you have a sibling, parent or child with colorectal cancer then you are at high risk. The risk is even greater if many of your family members have had the cancer.
3. Personal history of adenomatous polyps, colorectal cancer, Crohn’s disease or ulcerative colitis increases your chances of having the cancer.
4. Regular consumption of low-fiber, high-fat diets: Processed meat and red meat diets have been associated with colorectal cancer while diets rich in vegetables and fruits reduce the risk of the cancer.
5. Being of African-American descent carries more risk than people of other races.
6. Certain inherited syndromes such as hereditary non-polyposis and familial adenomatous polyposis increase risk of colorectal cancer.
7. Sedentary lifestyle, heavy alcohol use, smoking, obesity and diabetes increase chances of getting colorectal cancer.
8. Radiation therapy for cancer: Previous treatment of the abdominal area with radiation may increase the risk of colorectal cancer.
Signs and symptoms of colorectal cancer
Colorectal cancer tends not to show any symptoms in the early stages of the disease. But when symptoms appear, they vary according to the location and size of the cancer. Common colorectal cancer symptoms include:
1. Change in bowel habits, such as alternating episodes of constipation and diarrhea, or variation in stool consistency, which lasts more than 4 weeks
2. Blood in stool or rectal bleeding.
3.Persistent abdominal discomfort including bloating, cramps or pain.
4. Fatigue or weakness.
5. Unexplained weight loss or anemia.
6. Feeling of abdominal fullness even after going for a while without eating.
7. Feeling that your bowel does not empty completely.
8. A lump in the back passage or in the tummy.
Since most of these symptoms may have many possible causes, it is important to see a doctor for a proper and timely diagnosis. If you notice symptoms such as blood in stool or persistent change in your bowel habits, have an appointment with your doctor immediately. It is also important to speak with your doctor about when to begin or how frequently to screen for colorectal cancer.
Screening and diagnosis of colon cancer
Doctors recommend screening as a way of detecting early stage colon cancer. Screening tests detect colorectal cancer in healthy people with no symptoms. When colon cancer is detected early, there is a greater chance for it being cured and for survival. People with average risk of colorectal cancer should begin screening at 50 while those with higher risk, such as people with family history of the cancer, should start screening sooner. American Indians and African-Americans should begin colorectal cancer screening before the age of 45. There are several screening and diagnostic options for colorectal cancer, each with its benefits and drawbacks. Talk to your doctor about tests that are appropriate for you.
Screening and diagnostic procedures include:
- Physical examination: The doctor will take your personal and medical history before using some special procedures such as the digital rectal exam (DRE) to evaluate your rectum for abnormal lumps.
Fecal occult blood: A test that looks for presence of blood in your stool (feces).
- Stool DNA test: This test looks for various DNA markers shed into stool by pre-cancerous polyps or colorectal cancers.
- Flexible sigmoidoscopy: A quick and painless examination of your rectum and sigmoid (last area of the colon just before the rectum) using a flexible, slender and lighted tube. If pre-cancerous polyps or colon cancer is detected, the doctor will perform a colonoscopy of the whole colon.
- Double-contrast barium enema X-ray: The rectum and colon are examined using X-rays of the bowels. Barium is used to fill and coat the inner lining of the bowel to produce a clear image of the colon and rectum. If anything abnormal is found, the doctor recommends a colonoscopy.
- Colonoscopy: A colonoscope is a longer, more flexible and slender tube than a sigmoidoscope. It comes with a monitor and video camera and helps the doctor to see the entire rectum and colon in order to discover any polyps or colon cancer.
- Computerized tomography (CT) scan: Helps to take clear images of the colon. It is less invasive, more accurate and better-tolerated than conventional colonoscopy.
- Biopsy: To confirm colorectal cancer, the doctor will remove a tissue sample from the rectum or colon during a sigmoidoscopy or colonoscopy and send to a pathology laboratory for examination under a microscope.
- Ultrasound scan: Used to detect the extent of spread of colorectal cancer to other parts of the body.
- Magnetic resonance imaging (MRI): Provides 3-dimensional images of the bowel which help the doctor with diagnosis and treatment of the cancer.
Staging of colorectal cancer
After you have been diagnosed with colorectal cancer, the doctor will request tests to determine the stage (extent of spread) of the cancer. Staging helps to select the most appropriate treatment for the cancer. These include abdominal and chest CT scans, among other tests.
The stages of colorectal cancer are:
- Stage 0 (Duke A stage): Earliest stage of colon cancer, when it is still confined to the inner layer (mucosa) of the rectum or colon.
- Stage I (Duke B stage): The cancer has grown past (through) the mucosa (superficial lining) of the rectum or colon, but has not spread beyond the wall of the rectum or colon.
- Stage II (Duke C stage): The cancer has grown into or beyond the rectum or colon wall but has not reached the nearby lymph nodes.
- Stage III (Duke D stage): The cancer has spread into nearby lymph nodes but not yet spread to other parts of the body.
- Stage IV (Duke E stage): The cancer has reached various parts of the body, such as liver, lung, ovary or membrane lining of the abdominal cavity.
- Recurrent colorectal cancer: Cancer which has returned (re-occurred) after treatment. The cancer may come back and affect the colon, rectum or any other part of the body.
Treatments for colorectal cancer
There are various treatment options for colon cancer, depending on the size, stage and location of the cancer. Treatment also depends on whether or not the cancer is recurrent and on the current health status of the patient. Before any given treatment is selected, the doctor will explain all the options to you, allow you to ask questions and give you the chance to get appropriate lifestyle advice to boost your recovery.
Treatment options for colorectal cancer include:
1. Surgery is the most commonly used treatment for colorectal cancer. The tumor and affected lymph nodes are surgically removed to prevent further spread. However, the surgical procedure used depends on the stage of the cancer
2. Surgery for early-stage cancer
If the colorectal cancer is still very small and in its early stage, the doctor may apply a minimally-invasive surgical procedure to remove it. For example, if it is a small, localized and early-stage polyp, the doctor may completely remove it during a colonoscopy. For larger polyps requiring the removal of a portion of the mucosa (inner lining) of the colon or rectum, the doctor will use a procedure known as endoscopic mucosal resection. For some larger polyps that cannot be removed during colonoscopy, the doctor will use laparoscopic surgery, a minimally-invasive procedure involving several small incisions.
3. Surgery for invasive colorectal cancer
If the colorectal cancer has grown through or into the colon or rectum, the surgeon may consider various colostomy procedures. For example, the surgeon may do a partial colostomy, removing part of the colon or rectum that contains the cancer, together with margins of normal tissue on the sides of the cancer. The surgeon will then reconnect the healthy portions of the rectum or colon together. Another option is to create a channel for wastes to leave the body by performing a temporary or permanent colostomy. A surgeon can also remove nearby lymphs nodes and test them for colorectal cancer
4. Surgery for advanced colorectal cancer
If your health is very poor or your cancer is very advanced, the doctor can opt for surgery to relieve symptoms (such as pain and bleeding) instead of curing the cancer. For example, surgery may be done to remove any blockage to the colon or to remove a cancerous lesion from your liver. For more effectiveness, chemotherapy is used either before or after this kind of surgery.
Chemotherapy means using medicines (drugs) to kill or destroy cancerous cells. Chemotherapy is often used either before surgery or after surgery. When used before surgery, chemotherapy is intended to shrink the cancer and stop its spread. But when used after surgery, the intention is to control the spread of the cancer or prevent cancer recurrence. Chemotherapy is also used to relieve symptoms in patients with very poor health or in whom cancer has spread extensively to other parts of the body. For successful treatment of rectal cancer, chemotherapy is used together with radiation therapy before and after surgery.
Targeted drug therapy
A doctor may also prescribe drugs that are targeted at certain defects in cancer cells, curtailing the growth of such cells. Examples of targeted drugs are bevacizumab (Avastin), cetuximab (Erbitux), panitumumab (Vectibix), ramucirumab (Cyramza), regorafenib (Stivarga) and Ziv-aflibercept (Zaltrap). Targeted drugs may be administered alone or together with chemotherapy, but they are typically reserved for patients in advanced stage of colorectal cancer.
Also called radiotherapy, radiation therapy means using powerful high-energy beams, such as X-rays, to destroy or stop the multiplication of cancer cells. Radiotherapy is often used to kill cancerous cells that remain after surgery, to control cancer growth, to relieve cancer symptoms (such as pain), to shrink larger tumors prior to surgery, or to cure colorectal cancer. When safely and effectively administered, radiotherapy damages the ability of cancer cells to multiply and causes them to die and be removed naturally by the body. While healthy cells may be affected by the radiation, they are able to undergo repair in ways that cancer cells cannot.
Radiotherapy is hardly used for early-stage colon cancer, but is regularly used for rectal cancer that has penetrated the rectum wall or reached the lymph nodes. A combination of radiotherapy and chemotherapy is often used before surgery to make the operation easier, reduce the need for an ostomy later on and prevent the recurrence of the cancer.
When recommended, radiotherapy is delivered either externally (external beam radiotherapy) or internally (brachytherapy). External beam radiotherapy is the use of a series of daily outpatient treatments delivered accurately to the affected area from a source placed outside the body. Brachytherapy is the use of radiation delivered from a source placed surgically near the affected area. Brachytherapy is not commonly used in treating colorectal cancer.
During external beam radiotherapy, the radiation beam is delivered from an external machine called linac or linear accelerator. Before treatment begins, a simulation session is conducted to map out the affected area. During simulation, imaging is done using a CT scan or X-rays while a delineation technique such tattooing is used to precisely position the patient for treatment. To reduce potential side effects, treatment is delivered 5 days a week (Monday through Friday) for about 6 weeks to allow for delivery of adequate radiation into the body to kill the tumor while also giving healthy cells a break to recover from radiation. And with newer technologies such as intensity-modulated radiation therapy (IMRT) and 3-dimensional conformal radiotherapy (3D-CRT), radiotherapy can now be delivered with more precision, efficacy and safety.
Recovery from colorectal cancer
Colorectal cancer will most likely spread to other parts of the body if not treated. But when treated at an early stage, the chances of a complete cure increase immensely. Factors that affect recovery from colorectal cancer include:
1. Stage of the cancer when diagnosis was made.
2. Whether the cancer has recurred.
3. Whether there was a blockage or hole created in the colon by the cancer.
4. The overall health status of the patient.
Cancer treatments can take a toll on the body both physically and mentally. Therefore, make sure you take care of yourself through:
1. Plenty of rest.
2. Balanced, nutritious diet.
3. Following the instructions of your doctor.
4. Treatment of the skin area exposed to radiation.
5. Seeking support from your family, friends and cancer support networks.