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What is Colon/Rectum (Colorectal) Cancer?
Colorectal cancer begins when normal cells in the lining of the colon or rectum change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body). These changes usually take years to develop; however, when a person has an uncommon inherited syndrome, changes can occur within months to years. Both genetic and environmental factors can cause the changes.
Anatomy of the colon and rectum
The colon and rectum make up the large intestine, which plays an important role in the body's ability to process waste. The colon makes up the first five to six feet of the large intestine, and the rectum makes up the last six inches, ending at the anus.
The colon has four sections. The ascending colon is the portion that extends from a pouch called the cecum (the beginning of the large intestine into which the small intestine empties) on the right side of the abdomen. The transverse colon crosses the top of the abdomen. The descending colon takes waste down the left side. Finally, the sigmoid colon at the bottom takes waste a few more inches, down to the rectum. Waste leaves the body through the anus.
About colorectal polyps
Colorectal cancer most often begins as a polyp, a noncancerous growth that may develop on the inner wall of the colon or rectum as people get older. If not treated or removed, a polyp can become a potentially life-threatening cancer. Recognizing and removing precancerous polyps can prevent colorectal cancer.
There are several forms of polyps. Adenomatous polyps, or adenomas, are growths that may become cancerous and can be detected with a colonoscopy . Polyps are most easily found during colonoscopy because they usually bulge into the colon, forming a mound on the wall of the colon that can be found by the doctor.
About 10% of colon polyps are flat and hard to find with a colonoscopy, unless a dye is used to highlight them. These flat polyps have a high risk of becoming cancerous, regardless of their size.
Types of colorectal cancer
Colorectal cancer can begin in either the colon or the rectum. Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer.
Most colon and rectal cancers are a type of tumor called adenocarcinoma, which is cancer of the cells that line the inside tissue of the colon and rectum. This section specifically covers adenocarcinoma. Other types of cancer that occur far less often but can begin in the colon or rectum include carcinoid tumor, gastrointestinal stromal tumor (GIST), and lymphoma.
Symptoms & Signs
It’s important to remember that the symptoms and signs of colorectal cancer listed in this section are the same as those of extremely common noncancerous conditions, such as hemorrhoids and irritable bowel syndrome. When cancer is suspected, these symptoms usually have begun recently, are severe and long lasting, and change over time. By being alert to the symptoms of colorectal cancer, it may be possible to detect the disease early, when it is most likely to be treated successfully. However, many people with colorectal cancer do not have any symptoms until the disease is advanced, so people need to be screened regularly. People with colorectal cancer may experience the following symptoms or signs. As mentioned above, it is also possible that these symptoms may be caused by a medical condition that is not cancer, especially for the general symptoms of abdominal discomfort, bloating, and irregular bowel movements.
A change in bowel habits
Diarrhea, constipation, or feeling that the bowel does not empty completely
Bright red or very dark blood in the stool
Stools that look narrower or thinner than normal
Discomfort in the abdomen, including frequent gas pains, bloating, fullness, and cramps
Weight loss with no known explanation
Constant tiredness or fatigue
Unexplained iron-deficiency anemia (low number of red blood cells)
Talk with your doctor if these symptoms last for several weeks or become more severe. And talk with your doctor if you are concerned about any symptom or sign on this list and ask to schedule a colonoscopy to find the underlying reason(s).
Since colon cancer can occur in people younger than the recommended screening age and in older people between screenings, anyone at any age who experiences these symptoms should be evaluated by a doctor, to determine if he/she should have a colonoscopy.
Your doctor will ask you questions about the symptoms you are experiencing to help find out the cause of the problem, called a diagnosis. This may include how long you’ve been experiencing the symptom(s) and how often.
If cancer is diagnosed, relieving symptoms and side effects remains an important part of cancer care and treatment. This may also be called symptom management, palliative care, or supportive care. Be sure to talk with your health care team about symptoms you experience, including any new symptoms or a change in symptoms.
Risk Factors and Prevention
A risk factor is anything that increases a person’s chance of developing cancer. Although risk factors often influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. However, knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.
The cause of colorectal cancer is not known, but certain factors appear to increase the risk of developing the disease. The following factors may raise a person’s risk of developing colorectal cancer:
Age. The risk of colorectal cancer increases as people get older. Colorectal cancer can occur in young adults and teenagers, but more than 90% of colorectal cancers occur in people older than 50. The average age of diagnosis in the United States is 72.
Family history of cancer. Colorectal cancer is more likely to develop in a person who has had a parent, sibling, or child with colorectal cancer, particularly if the family member was diagnosed with colorectal cancer before age 60. Members of families with certain uncommon inherited conditions also have a significantly increased risk of colorectal cancer; these include familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (AFAP), Gardner syndrome, hereditary nonpolyposis colorectal cancer (HNPCC), Juvenile Polyposis syndrome (JPS), Muir-Torre syndrome, MYH-associated polyposis (MAP), Peutz-Jeghers syndrome (PJS), and Turcot syndrome. Relatives of women with uterine cancer may also be at higher risk.
Inflammatory bowel disease (IBD). People with IBD, such as ulcerative colitis or Crohn’s disease, may develop chronic inflammation of the large intestine, which increases the risk of colon cancer. IBD is not the same as irritable bowel syndrome.
Adenomatous polyps (adenomas). Polyps are not cancer, but some types of polyps called adenomas are most likely to develop into colorectal cancer. Polyps can often be completely removed using a tool during a colonoscopy, a test in which a doctor looks into the colon using a lighted tube after the patient has been sedated. Polyp removal can prevent colon cancer. People who have had adenomas have a greater risk of additional polyps and of colon cancer, and they should have follow-up screening tests regularly (see below).
Personal history of certain types of cancer. People with a personal history of colon cancer and women who have had ovarian cancer or uterine cancer are more likely to develop colon cancer.
Race. Black people have the highest rates of sporadic (non-hereditary) colorectal cancer in the United States, and colon cancer is a leading cause of cancer-related deaths among black people. Black women are more likely to die from colorectal cancer than women from any other racial group, and black men are even more likely to die from colorectal cancer than black women. The reasons for these differences are unclear. Noting that black people are more likely to be diagnosed with colon cancer at a younger age, the American College of Gastroenterology suggests that black people begin screening with colonoscopies at age 45 (see below). Earlier screening may find changes in the colon at a more treatable stage.
Physical inactivity and obesity. People who lead an inactive lifestyle (no regular exercise and a lot of sitting) and people who are overweight may have an increased risk of colorectal cancer.
Smoking. Recent studies have shown that smokers are more likely to die from colorectal cancer than nonsmokers.
The following may lower a person’s risk of colorectal cancer:
Nonsteroidal anti-inflammatory drugs (NSAIDs). Some studies suggest that aspirin and other NSAIDs may reduce the development of polyps in people with a history of colorectal cancer or polyps. However, regular use of NSAIDs may cause major side effects, including bleeding of the stomach lining and blood clots leading to stroke or heart attack. Taking aspirin or other NSAIDs cannot be substituted for regular colorectal cancer screening. People should talk with their doctor about the risks and benefits of taking aspirin on a regular basis.
Diet and supplements. A diet rich in fruits and vegetables and low in red meat may help reduce the risk of colon cancer. Some studies have also found that people who take calcium and vitamin D supplements have a lower risk of colorectal cancer.
Screening and Prevention
Colorectal cancer can often be prevented through regular screening, which can find precancerous polyps. Talk with your doctor about when screening should begin based on your age and family history of the disease. Although some people should be screened earlier, people of average risk should begin screening at age 50, and black people should start at age 45 (because they are more commonly diagnosed at a younger age). Because most colorectal cancer occurs without symptoms until the disease is advanced, it is important for people to talk with their doctor about the pros and cons of each screening test and how often each test should be given. Under these guidelines, people should begin colorectal cancer screening earlier and/or undergo screening more often if they have any of the following colorectal cancer risk factors:
A personal history of colorectal cancer or adenomatous polyps
A strong family history of colorectal cancer or polyps (cancer or polyps in a first-degree relative younger than 60 or in two first-degree relatives of any age). A first-degree relative is defined as a parent, sibling, or child.
A personal history of chronic inflammatory bowel disease
A family history of hereditary colorectal cancer syndromes (FAP, HNPCC, or other syndromes).
The tests used to screen for colorectal cancer are described below:
Colonoscopy. This test allows the doctor to look inside the entire rectum and colon while a patient is sedated. A colonoscope (a flexible, lighted tube) is inserted into the rectum and the entire colon to look for polyps or cancer. During this procedure, a doctor can remove polyps or other tissue for examination. This is the only screening test that allows the removal of polyps, which can also prevent colorectal cancer.
Computed tomography (CT or CAT) colonography. CT colonography (sometimes called virtual colonoscopy) is a screening method being studied in some centers. It requires interpretation by a skilled radiologist (a doctor who specializes in obtaining and interpreting medical images) to be used to the best advantage. However, it may be an alternative for people who cannot have a standard colonoscopy due to the risk of anesthesia or if a person has an obstruction in the colon that prevents a full examination.
Sigmoidoscopy. A sigmoidoscope (a flexible, lighted tube) is inserted into the rectum and lower colon to check for polyps, cancer, and other abnormalities. During this procedure, a doctor can remove polyps or other tissue for later examination. The doctor cannot check the upper part of the colon (ascending and transverse colon) with this test. If polyps or cancer is found using this test, a colonoscopy to view the entire colon is recommended.
Fecal occult blood test (FOBT). This is a test used to find blood in the feces (stool), which can be a sign of polyps or cancer. A positive FOBT test (meaning that blood is found in the feces) can be from causes other than a colon polyp or cancer, including bleeding in the stomach or upper GI tract and even ingestion of rare meat or other foods. There are two types of tests: guaiac and immunochemical. Polyps and cancers do not bleed continually, so the FOBT must be done on several stool samples each year and should be repeated each year. Even then, the reduction in deaths from colorectal cancer is fairly small (around 30% if done yearly and 18% if done every other year).
Double contrast barium enema (DCBE). For patients who cannot have a colonoscopy, an enema containing barium is given, which helps the outline of the colon and rectum stand out on x-rays. A series of x-rays is then taken of the colon and rectum. In general practice, most doctors would recommend other screening tests because a barium enema has a lower likelihood of detecting precancerous polyps than a colonoscopy, sigmoidoscopy, or CT colonography.
Stool DNA tests. This test analyzes the DNA from a person’s stool sample to look for cancer. It uses changes in the DNA that occur in polyps and cancers to determine whether a colonoscopy should be done.
Different organizations have made different recommendations for colorectal cancer screening. Talk with your doctor about the best test and time between tests based on your health history and personal cancer risk.
The American Gastroenterological Association, the American College of Gastroenterology, the American Society for Gastrointestinal Endoscopy, the American Cancer Society, and the American College of Radiology have developed consensus guidelines for screening for colorectal cancer, with the goal of cancer prevention.
Beginning at age 50, both men and women of average risk should follow one of these testing schedules.
The following tests detect both polyps and cancer:
Flexible sigmoidoscopy, every five years
Colonoscopy, every 10 years
DCBE, every five years
CT colonography, every five years
These tests primarily detect cancer:
Guaiac-based FOBT, every year
Fecal immunochemical test, every year
Stool DNA test, as often as your doctor recommends
Guidelines for colon cancer screeningwhich differ somewhat from those mentioned above:
A high-sensitivity FOBT, every year
Sigmoidoscopy, every five years, with FOBT testing between tests
Colonoscopy, every 10 years
In addition, this task force did not think there was enough evidence of benefit or harm to recommend virtual colonography and fecal DNA testing.
Adults between ages 76 and 85 should not have routine screening, because the risks outweigh the benefits, and adults older than 85 can forgo colorectal cancer screening.
It is important to note that, regardless of the screening test and schedule, any test that indicates an abnormality should be followed up with a colonoscopy.
Doctors use many tests to diagnose cancer and to find out if it has metastasized (spread). Some tests may also determine which treatments may be the most effective. For most types of cancer, a biopsy is the only way to make a definitive diagnosis of cancer. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis. Imaging tests may be used to find out whether the cancer has metastasized. Your doctor may consider these factors when choosing a diagnostic test
Age and medical condition
Type of cancer suspected
Severity of symptoms
Previous test results
In addition to a physical examination, the following tests may be used to diagnose colorectal cancer. The doctor will also ask about the person's medical and family history.
Colonoscopy. As described in Screening, this test allows the doctor to look inside the entire rectum and colon while a patient is sedated. A colonoscopist is a doctor who specializes in performing this test. If colorectal cancer is present, a complete diagnosis that accurately describes the location and spread of the cancer may not be possible until the tumor is surgically removed.
Biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis of colorectal cancer. The sample removed from the biopsy is analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease). A biopsy may be performed during a colonoscopy, or it may be done on any tissue that is removed during surgery. Sometimes, a CT scan or ultrasound is used to help perform a needle biopsy (removing tissue through the skin with a needle that is guided into the tumor).
Molecular testing of the tumor. Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Results of these tests will help decide whether your treatment options include a type of treatment called targeted therapy .
Blood tests. Because colorectal cancer often bleeds into the large intestine or rectum, people with the disease may become anemic. A test of the number of red cells in the blood, which is part of a complete blood count (CBC), can indicate that bleeding may be occurring.
Another blood test detects the levels of a protein called carcinoembryonic antigen (CEA). High levels of CEA may indicate that a cancer has spread to other parts of the body. CEA is not an absolute test for colorectal cancer because levels are high for only about 60% of people with colorectal cancer that has spread to other organs from the colon. In addition, other medical conditions can cause CEA to increase. CEA tests are most often used to monitor colorectal cancer for patients already receiving treatment and are not screening tests.
CT scan. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a patient’s vein to provide better detail. In a person with colon cancer, a CT scan can check for the spread of cancer in the lungs, liver, and other organs. It is often done before surgery.
Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. A contrast medium (a special dye) may be injected into a patient’s vein to create a clearer picture. MRI is the best imaging test to find where the colorectal cancer has grown.
Ultrasound. Ultrasound is a procedure that uses sound waves to create a picture of the internal organs to find out if cancer has spread. Endorectal ultrasound is commonly used to find out how deeply the rectal cancer has grown and can be used to help plan treatment; however, this test cannot accurately detect metastatic lymph nodes (cancer that has spread to nearby lymph nodes) or cancer that has spread beyond the pelvis. Ultrasound can also be used to view the liver, although CT scans or MRIs (see above) are preferred because they are better for finding tumors in the liver.
Chest x-ray. An x-ray is a way to create a picture of the structures inside of the body, using a small amount of radiation. An x-ray of the chest can help doctors find out if the cancer has spread to the lungs.
Positron emission tomography (PET) scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient’s body. This substance is absorbed mainly by organs and tissues that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.
After these diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is cancer, these results also help the doctor describe the cancer; this is called staging.
Staging is a way of describing where the cancer is located, if or where it has spread, and whether it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine the cancer's stage, so staging may not be complete until all of the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis (chance of recovery). There are different stage descriptions for different types of cancer.
One tool that doctors use to describe the stage is the TNM system. This system judges three factors: the tumor itself, the lymph nodes around the tumor, and if the tumor has spread to other parts of the body. The results are combined to determine the stage of cancer for each person. There are five stages: stage 0 (zero) and stages I through IV (one through four). The stage provides a common way of describing the cancer, so doctors can work together to plan the best treatments.
TNM is an abbreviation for tumor (T), node (N), and metastasis (M). Doctors look at these three factors to determine the stage of cancer:
For colorectal cancer, “T” describes how deeply the primary (first) tumor has grown into the bowel lining. (Tumor, T)
Has the tumor spread to the lymph nodes? (Node, N)
Has the cancer metastasized to other parts of the body?(Metastasis, M)
Tumor. Using the TNM system, the "T" plus a letter or number (0 to 4) is used to describe how deeply the primary tumor has grown into the bowel lining. Some stages are also divided into smaller groups that help describe the tumor in even more detail. Specific tumor information is listed below.
TX: The primary tumor cannot be evaluated.
T0: There is no evidence of cancer in the colon or rectum.
Tis: Refers to carcinoma in situ (also called cancer in situ). Cancer cells are found only in the epithelium or lamina propria (the top layers lining the inside of the colon or rectum).
T1: The tumor has grown into the submucosa (the layer of tissue underneath the mucosa or lining of the colon).
T2: The tumor has grown into the muscularis propria (a deeper, thick layer of muscle that contracts to force the contents of the intestines along).
T3: The tumor has grown through the muscularis propria and into the subserosa (a thin layer of connective tissue beneath the outer layer of some parts of the large intestine) or into tissues surrounding the colon or rectum.
T4a: The tumor has grown into the surface of the visceral peritoneum (through all layers of the colon).
T4b: The tumor directly has grown into or has attached to other organs or structures.
Node. The "N" in the TNM system stands for lymph nodes. The lymph nodes are tiny, bean-shaped organs that are located throughout the body that help the body fight infections as part of the immune system. Lymph nodes near the colon and rectum are called regional lymph nodes. All others are distant lymph nodes (lymph nodes found in other parts of the body).
NX: The regional lymph nodes cannot be evaluated.
N0: There is no spread to regional lymph nodes.
N1a: There are tumor cells found in one regional lymph node.
N1b: There are tumor cells found in two to three regional lymph nodes.
N1c: There are nodules made up of tumor cells found in the structures near the colon that do not appear to be lymph nodes.
N2a: There are tumor cells found in four to six regional lymph nodes.
N2b: There are tumor cells found in seven or more regional lymph nodes.
Distant metastasis. The "M" in the TNM system describes cancer that has spread to other parts of the body (such as the liver or lungs).
MX: Distant metastasis cannot be evaluated.
M0: The disease has not spread to a distant part of the body.
M1a: The cancer has spread to one other part of the body beyond the colon or rectum.
M1b: The cancer has spread to more than one part of the body other than the colon or rectum.
Cancer stage grouping
Doctors assign the stage of the cancer by combining the T, N, and M classifications.
Stage 0: This is called cancer in situ. The cancer cells are only in the mucosa (the inner lining) of the colon or rectum.
Stage I: The cancer has grown through the mucosa and has invaded the muscular layer of the colon or rectum. It has not spread into nearby tissue or lymph nodes (T1 or T2, N0, M0).
Stage IIA: The cancer has grown through the wall of the colon or rectum and has not spread to nearby tissue or to the nearby lymph nodes (T3, N0, M0).
Stage IIB:The cancer has grown through the layers of the muscle to the lining of the abdomen (called the visceral peritoneum). It has not spread to the nearby lymph nodes or elsewhere (T4a, N0, M0).
Stage IIC:The tumor has spread through the wall of the colon or rectum and has grown into nearby structures. It has not spread to the nearby lymph nodes or elsewhere (T4b, N0, M0).
Stage IIIA: The cancer has grown through the inner lining or into the muscle layers of the intestine and spread to one to three lymph nodes, or to a nodule of tumor in tissues around the colon or rectum that do not appear to be lymph nodes but has not spread to other parts of the body (T1 or T2; N1 or N1c, M0 or T1, N2a, M0).
Stage IIIB: The cancer has grown through the bowel wall or to surrounding organs and into one to three lymph nodes or to a nodule of tumor in tissues around the colon or rectum that do not appear to be lymph nodes, but has not spread to other parts of the body (T3 or T4a, N1 or N1c, M0; T2 or T3, N2a, M0; or T1 or T2, N2b, M0).
Stage IIIC:The cancer of the colon, regardless of how deep it has grown, has spread to four or more lymph nodes, but not to other distant parts of the body (T4a, N2a, M0; T3 or T4a, N2b, M0; or T4b, N1 or N2, M0).
Stage IVA: The cancer has spread to a single distant part of the body, such as the liver or lungs (any T, any N, M1a).
Stage IVB: The cancer has spread to more than one part of the body (any T, any N, M1b).
Recurrent: Recurrent cancer is cancer that has come back after treatment. The disease may be found in the colon, rectum, or in another part of the body. If there is a recurrence, the cancer may need to be staged again (called re-staging) using the system above.
Tumor grade (G). Doctors may also use the term "grade," which describes how much the tumor appears like normal tissue. The grade of a cancer can help the doctor predict how quickly the cancer might grow. In cancer that resembles normal tissue, doctors can clearly see different types of cells grouped together. In a higher-grade cancer, the cancer cells usually look less like normal cells, or "wilder"). In general, a lower-grade cancer means a better prognosis.
GX: The tumor grade cannot be identified.
G1: The cells are more like normal cells (called well differentiated).
G2: The cells are somewhat like normal cells (called moderately differentiated).
G3: The cells look less like normal cells (called poorly differentiated).
G4: The cells barely look like normal cells (called undifferentiated).
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