Cancer that begins in the colon is called a colon cancer, while cancer in the rectum is known as a rectal cancer. Cancers that affect either of these organs may be called colorectal cancer. Though not true in all cases, the majority of colorectal cancers generally develop over time from adenomatous (precancerous) polyps. Polyps (growths) can change after a series of mutations (abnormalities) arise in their cellular DNA. Some of the risk factors for colorectal cancer involve a family history of colon or rectal cancer, diet, alcohol intake, smoking and inflammatory bowel disease.
To understand colorectal cancer, it is helpful to understand what parts of the body are affected and how they work.
The colon is an approximately 5- to 6-foot long tube that connects the small intestine to the rectum. The colon—which along with the rectum is called the large intestine—moves and processes digesting food across your body and down towards the rectum, where it exits the body as stool. There are several parts of the colon, including:
The rectum is a 5- to 6-inch chamber that connects the colon to the anus. It is the job of the rectum to act as a storage unit and hold the stool until defecation (evacuation) occurs.
All of the body's cells normally grow, divide, and then die in order to keep the body healthy and functioning properly. Sometimes this process gets out of control. Cells keep growing and dividing even when they are supposed to die. When the cells lining the colon and rectum multiply uncontrolled, colorectal cancer may ultimately develop.
Fortunately, most colorectal cancers begin as small precancerous (adenomatous or serrated) polyps. These polyps usually grow slowly and do not cause symptoms until they become large or cancerous. This allows the opportunity for detection and removal at this pre-cancerous polyp stage before the development of cancer.
There are a variety of colorectal polyps, but cancer is thought to arise mainly from adenomas and sessile serrated lesions, which are precancerous polyps. If a polyp is found during a colonoscopy it is usually removed, if possible. Polyps removed during colonoscopies are then examined by a pathologist and evaluated to determine if they contain cancerous or precancerous cells. Based on the number, size, and type of precancerous polyps found during colonoscopy, your healthcare provider will recommend a future colonoscopy for monitoring (surveillance).
Unfortunately, some colorectal cancers might be present without any signs or symptoms. For this reason, it is very important to have regular colorectal screenings (examinations) to detect problems early. The best screening evaluation is a colonoscopy. Other screening options include fecal occult blood tests, fecal DNA tests, flexible sigmoidoscopy, barium enema, and CT colonography (virtual colonoscopy). The age at which such screening tests begin depends upon your risk factors, especially a family history of colon and rectal cancers.
Even if you do not have a family history of colorectal cancer or polyps, tell your doctor if you have any of the signs that could indicate a colorectal cancer, no matter what your age. Common signs of colorectal cancer include the following:
If you experience any of these signs or symptoms, it is important to see your doctor for evaluation. For a patient with colorectal cancer, early diagnosis and treatment can be life-saving.
The American Cancer Society recommends that people at average risk of colorectal cancer start regular screening at age 45. Other experts recommend regular screening in average risk individuals to start no later than at age 50. However, if you have a personal or a family history of colorectal polyps or cancer, or inflammatory bowel disease, screening may need to begin before age 45. Men and women should undergo screening since colorectal polyps and cancer affect both genders. Ask your healthcare provider what age is best to start your screening based on your personal risk factors.
Your doctor may recommend earlier screening for colorectal cancer if you have a family history of the condition. To determine the appropriate age to start screening, your doctor will discuss all of your risk factors with you. These risk factors can include a family or personal history of polyps, a history of cancer in the abdomen, and a history of inflammatory bowel disease.
Some studies have found that having a first-degree relative with colorectal cancer puts you at a risk that is 2-3 times higher than someone without a first-degree relative with colorectal cancer. A first-degree relative is defined as your mother, your father, your brother or sister, and your child. Your risk can also be higher if you have other people in your family with colorectal cancer, even if they are not first-degree relatives. They could be grandparents, aunts, uncles, cousins, nieces and nephews, even grandchildren.
The age at which any relative is diagnosed is also important. The risk to you is more significant when the relative is diagnosed before age 45.
About 75% of people who do get colorectal cancer do not get it because of genetics. About 10% to 30% do have a family history of the disease.
If you do have relatives that have been diagnosed with colorectal cancer, your healthcare provider may also recommend genetic testing and/or genetic counseling. Certain DNA mutations are inherited and are linked to colorectal cancers. Genetic testing may provide the information needed to know if you are at a higher risk, so that you can have the correct screening at the right time and possibly stop cancer before it develops or at a very early stage.
Several tests are used to screen for colorectal cancer. Although colonoscopy is most recommended, other options are available. These are the most common screening tests:
Colorectal cancer can be diagnosed by a variety of tests. This condition can be diagnosed after you show symptoms or if your caregiver finds something during a screening test that is not normal.
During the diagnosis process, your doctor may do the following tests:
Routine screening tests are done before you show any symptoms. These tests are detailed above.
Colorectal cancer is treated based on the stage of cancer. Staging identifies the severity of the cancer. Treatment options can include the use of surgery, chemotherapy and radiation.
Colorectal cancer is described clinically by the stages at which it is discovered. The various stages of a colorectal cancer are determined by the depth of invasion through the wall of the intestine; the involvement of the lymph nodes (the drainage nodules); and the spread to other organs (metastases). Listed below is a description of the stages of colorectal cancer and the treatment for each stage. In most cases, treatment requires surgical removal (resection) of the affected part of the intestine. For some tumors, chemotherapy or — for rectal cancers — radiation are added to manage the disease.
Stage 0: For lesions that are stage 0 — also known as carcinoma in situ — the disease remains within the lining of the colon or rectum. Lesions are in the pre-cancerous stage and are not cancers. Therefore, removal of the lesion, either by polypectomy via colonoscopy or by surgery if the lesion is too large, may be all that is required for treatment.
Stage I: Stage I colorectal cancers have grown into the wall of the intestine but have not spread beyond its muscular coat or into close lymph nodes. The standard treatment of a stage I colon cancer is usually a colon resection alone, in which the affected part of the colon and its lymph nodes are removed. The type of surgery used to treat a rectal cancer is dependent upon its location, but includes a low anterior resection or an abdominoperineal resection.
Stage II: Stage II is divided into three smaller stages. In the first stage, IIA, the cancer has spread through the wall of the colon. In stage IIB, colorectal cancer has penetrated beyond the muscular layers of the large intestine. By stage IIC the cancer has even spread into adjacent tissue. However, in all stage II lesions, the cancer has not yet reached the lymph nodes. Usually the only treatment for this stage of colon cancer is a surgical resection (removal), although chemotherapy after surgery may be added. For a stage II rectal cancer, a surgical resection is sometimes preceded or followed by chemotherapy and/or radiation.
Stage III: A stage III colorectal cancer is considered an advanced stage of cancer as the disease has spread to the lymph nodes. Once again, there are three smaller stages of stage III colorectal cancer. Stage IIIA is characterized by cancer that has moved beyond the colon wall and spread to one to three lymph nodes or a very early lesion in the colon wall that has spread to four to six lymph nodes. In the second stage, IIIB, more lymph nodes are affected or there is a more advanced lesion in the colon wall with one to three lymph nodes affected. The cancer also impacts the organs in the abdomen in this stage. In stage IIIC, the cancer continues to spread to nearby lymph nodes and impacts more adjacent tissue of organs in the abdomen. For a colon cancer, surgery is usually done first, followed by chemotherapy. Chemotherapy and radiation may precede or follow surgery for a stage III rectal cancer.
Stage IV: For patients with stage IV colorectal cancer, the disease has spread (metastasized) to distant organs such as the liver, lungs or ovaries. This stage is also divided into three stages. Stage IVA is characterized by cancer that has spread to an organ and lymph nodes that are farther from the colon. In stage IVB the cancer has moved to more than one distant organ and more lymph nodes. Stage IVC cancer has impacted not only the distant organs and lymph nodes, but also the tissue of the abdomen. When the cancer has reached this stage, surgery is generally used for relieving or preventing complications as opposed to curing the patient of the disease. Occasionally the cancer's spread is restricted enough to where it can all be removed by surgery. In the case of minimal disease in the liver, the tumor may be treated with radiofrequency ablation (destruction with heat), cryotherapy (destruction by freezing), or intra-arterial chemotherapy. For stage IV cancer that cannot be surgically removed, chemotherapy, radiation therapy, or both may be used to relieve, delay, or prevent symptoms.
Chemotherapy refers to drugs that kill cancer cells. Chemotherapy drugs can be given intravenously (into a vein) via an injection or a pump, or orally (by mouth) as a pill. Each drug works against a specific cancer and is delivered in specific doses and schedules. Chemotherapy may be recommended for advanced colorectal cancers, in which the cancer cells have spread to the lymph nodes (drainage nodules) or to other organs.
Chemotherapy is used in the following ways:
Your doctor will talk with you about the best treatment for your condition.
5-Fluorouracil, or 5-FU (Adrucil®), has been the first-line chemotherapy drug, along with the vitamin leucovorin, for advanced colorectal cancers for many years. 5-FU is often given intravenously but is also available in an oral form as capecitabine (Xeloda®).
Two other intravenous (directly into the vein) chemotherapy drugs — irinotecan (Camptosar®) and oxaliplatin (Eloxatin®) — also are used for the treatment of advanced colorectal cancers. Oxaliplatin is given, along with 5-FU and leucovorin, for advanced colorectal cancers, while irinotecan is used alone or in combination with 5-FU/leucovorin for patients with metastatic colorectal cancer (cancer that has spread).
Newer treatments for metastatic colorectal cancer include monoclonal antibodies and immunotherapy.
Monoclonal antibodies are created in a lab to find and destroy a particular target – in this case, colorectal cancer cells. Because of their precision, the idea is that treating a tumor with a monoclonal antibody will be more specific than chemotherapy drugs, and therefore have fewer side effects.
Some monoclonal antibody medications prevent tumors from growing the blood vessels needed for their survival, such as vascular endothelial growth factor (VEGF), a substance released by tumors to stimulate the growth of new blood vessels. Interfering with the blood supply to a tumor might slow its growth. Others slow cancer growth by targeting the epidermal growth factor receptor (EGFR), a protein found on the surface of about 60 to 80 percent of colon cancer cells. They are often used along with or after other chemotherapy agents for metastatic colorectal cancer that does not respond to other treatments.
Immunotherapy is a newer type of treatment for colorectal cancer. The goal of immunotherapy is to boost a patient’s immune reaction to the cancer cells to help them fight the disease more effectively. There are two types of immunotherapy: active and passive.
The side effects of traditional chemotherapy depend upon the drug, its dosage, how long the treatment lasts and the patient. Because traditional chemotherapy drugs target rapidly dividing cancer cells, they also kill other rapidly dividing healthy cells in the lining of the mouth and the gastrointestinal tract, the hair follicles, and the bone marrow. The side effects of chemotherapy come from damage to these normal cells. (Although hair loss is not common to most chemotherapy treatments for colorectal cancer, some people may experience hair thinning.)
The side effects of traditional chemotherapy can include:
Since chemotherapy affects the bone marrow, there may also be a greater risk of infection (because of low white blood cell counts), bleeding or bruising from minor injuries (because of low blood platelet counts), and anemia-related fatigue (because of low red blood cell counts).
Although it may take some time, most side effects related to chemotherapy will go away when the chemotherapy is stopped.
The side effects of monoclonal antibodies depend on the drug. Many of these side effects are similar to those of traditional chemotherapy medications.
Ask your doctor about the side effects of any medications before you start to take them. If you are having any side effects, tell your doctor. In many cases, they can be treated or prevented with medications or a change in diet.
Every one of us is at risk for colorectal cancer. Although the exact cause for the development of precancerous colon polyps that lead to colorectal cancer is not known, there are some factors that increase a person's risk of developing colorectal polyps and cancer. These risk factors include:
Having one or more of these risk factors does not guarantee that you will develop colorectal cancer. However, you should talk about these risk factors with your doctor. He or she may be able to suggest ways to reduce your chances of developing colorectal cancer.
Every person is different and responds differently to treatment. However, with prompt and appropriate treatment, the outlook for a person with colorectal cancer is hopeful. The survival rate for people with colorectal cancer depends on the stage of the cancer at the time of diagnosis and the individual’s response to treatment. In addition, many new discoveries have the potential for improving the treatment of colorectal cancer, as well as the prognosis.
Several factors determine how well a person will do after treatment for colorectal cancer. They include:
Many people who have had colorectal cancer live normal lives. The treatments available today offer good outcomes, but you may require several treatments or a combination of treatments (surgery, chemotherapy, radiation) to have the best chance of avoiding a recurrence of the cancer. Remember to tell your doctor about any changes in your health. This will help him or her decide if you need any additional screening tests or treatment.
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Last reviewed by a Cleveland Clinic medical professional on 04/22/2020.