Written by Ada’s Medical Knowledge Team
What is colorectal cancer?
Colorectal cancer, also known as bowel cancer, is a cancer that begins in the large intestine, the endpoint of the body’s digestive system, which food waste travels through, before exiting the body.
Most of the large intestine is called the colon. The final part that food travels through before exiting the body as stool is called the rectum. Seven out of ten cancers of the large intestine begin in the colon, while the remainder start in the rectum. Colorectal cancer is the fourth most common cancer in the U.S.
Symptoms of colorectal cancer depend on how large the cancer has grown and how far it has spread. There are likely to be no symptoms in the early stages of colorectal cancer, which is why attending regular screening is important. When symptoms begin, they may include blood and mucus being visible in feces, as well as an uncomfortable feeling in the bowel.
Colorectal cancer is more likely to affect people when they are over 50. It is also more likely to affect a person whose family has a history of colorectal cancer. Certain inherited conditions, such as Lynch syndrome and familial adenomatous polyposis (FAP), are strong risk factors, but these are very rare. Avoidable risk factors include obesity, smoking tobacco products and low levels of exercise.
The cancer is diagnosed through certain tests that allow a doctor to look inside a person’s large intestine. This can be achieved by inserting a camera into a person’s body, such as in a colonoscopy or by using X-rays.
Surgery is normally the only way to cure colorectal cancer. However, depending on how developed the cancer is, surgery may no longer be an option for some people. In those cases, medication can be used to manage symptoms and attempt to prolong a person’s life.
The best way to prevent the more dangerous forms of colorectal cancer is to attend regular screening for the condition.
Colorectal cancer is unlikely to cause any symptoms initially. Early stage colorectal cancer is usually detected through regular screening, rather than through any suspicion that the person has the condition.
- Blood or mucus in the feces
- Changes in bowel habits, such as having diarrhea or being constipated
- A feeling of needing a bowel movement that does not go away after having one
- Pain from gas, bloating, cramps or a feeling of being full
- Bleeding from the anus
- Iron-deficiency anemia
- Unexplained and/or unintended weight loss
- Tiredness or feeling weaker than normal
- Iron-deficiency anemia
Tumors in the left side or latter part of the colon are more likely to cause the feeling of bowel obstruction. They are also likely to be detected later on than ones in the right side.
The majority of colorectal cancer develops out of small clumps of tissue, known as polyps, that form out of the lining of the large intestine. Colon polyps are very common, affecting between 20 and 30 percent of adults in the U.S. at some point in their lives, and most will never become cancerous. Non-cancerous polyps are also called benign polyps.
Benign polyps mutate into cancerous or malignant polyps due to a change in their gene chemistry. This is usually due to the activation of a gene in a cell that makes it more likely to develop cancer. However, it may also be caused by genes that help prevent the development of cancer somehow becoming suppressed.
Once cells in the large intestine become cancerous, they can break away and spread to other parts of the body in a process known as metastasis. The cancer is usually spread through the lymphatic system or the bloodstream.
Genetically inherited conditions, preexisting health conditions and a person’s lifestyle can all be factors contributing to the development of cancer of the colon or rectum. Colorectal cancer is more likely to affect a person when they are over 50, but some younger people, especially those with certain health conditions, are at an increased risk.
A diagnosis of colorectal cancer is more likely if a family member has been affected by the condition in the past or has developed benign polyps in the colon before they are 60 years old.
Familial adenomatous polyposis (FAP) is a rare hereditary condition that prompts the development of hundreds or even thousands of polyps in the large intestine. If left untreated, people affected by this condition are almost certain to develop colorectal cancer by the age of 40. A milder version of FAP exists, called autosomal recessive familial adenomatous polyposis, in which dozens, rather than hundreds, of polyps form. A person with a family history of this condition or a family history of colorectal cancer more generally should be tested by a doctor. People affected by FAP should ideally start being screened for polyps when they are between 10 and 12 years of age.
Lynch syndrome or HNPCC carries a 40 percent lifetime risk for developing colorectal cancer. Lynch syndrome affects the ability of DNA to self-repair; this can lead to cells mutating and becoming cancerous.
Other genetically inherited conditions that lead to the formation of polyps in the bowel, such as hamartomatous polyposis syndrome, are a rare risk factor.
A person diagnosed with any of the above conditions will be a candidate for regular colorectal cancer screenings at a younger age.
- Are obese, particularly men
- Do not exercise regularly
- Consume high quantities of alcohol
- Smoke tobacco products
A diagnosis of diabetes mellitus or type 2 diabetes is also a risk factor for colorectal cancer.
The conversation about the contribution of dietary factors to colorectal cancer is continually evolving. However, there is strong evidence that the following increase the possibility of being affected by the condition:
- High intake of red and processed meat, as well as animal fats
- Low intake of fiber, particularly whole grain and cereal fiber
- Low intake of folate, found in broccoli, brussels sprouts, leafy greens
- Low intake of calcium, found in dairy products, leafy greens and nuts
- Low intake of fruit and vegetables generally
Eating more fermented dairy products, such as yoghurt and sour cream, offers some protection against colorectal cancer, research suggests.
Inflammatory bowel conditions
People with inflammatory bowel diseases (IBD), i.e. Crohn’s Disease and ulcerative colitis, are at increased risk of being affected by colorectal cancer. There seems to be a link between inflammation of the gut and the mutation of cancerous cells.[^17] As a result, the longer the person is affected by IBD, the greater the risk.
After a diagnosis of an IBD, a doctor will likely recommend a person for early colorectal cancer screening.
The earlier cancer is detected, the easier it is to be treated. Regular screening considerably lowers the risk of colorectal cancer reaching a more harmful stage.
if symptoms are present, then a person is likely to be physically examined and asked questions about what they have been experiencing before doctors run tests.
A colonoscopy is the most accurate test for colorectal cancer. In a colonoscopy, medical professionals use a thin and bendy tube, called an endoscope or colonoscope. This tube has a camera attached to the end that is used to examine the inside of the large intestine.
Before a colonoscopy, the entire colon and rectum needs to be cleaned out, usually by using laxative medications to provoke temporary diarrhea. The person’s diet may need to be restricted in the runup to the procedure. Sedation, a calming drug, is generally required during the procedure to avoid pain.
Polyps or other growths that are found can be removed using a wire loop attached to the endoscope. These growths can then be examined under a microscope in a process known as a biopsy.
A sigmoidoscopy is a less invasive version of a colonoscopy. This procedure also involves using a tube with a camera attached to the end to inspect the inside of the bowel. However, a sigmoidoscopy can only be used to assess the rectum and the lower part of the colon, known as the descending or sigmoid colon. A colonoscopy can look for evidence of cancer in the entirety of the large intestine.
Before a sigmoidoscopy, a person will need to evacuate their bowels. This generally involves avoiding solid foods beforehand, followed by an enema, which is when fluid is inserted through the rectum to provoke laxative effects.
A CT colonography is a CT scan of the large intestine. This is less invasive than a sigmoidoscopy or colonoscopy and also allows a doctor to assess the entirety of the bowels. A CT colonography may be recommended if a person is unable to undergo a colonoscopy.
Similarly to before a colonoscopy, laxatives will be required to clear out the bowels, and a restricted diet will need to be followed in the run-up to the procedure.
If cancer is suspected after a colonography, then it is likely that the person being tested will have to undergo a traditional colonoscopy as well. This is because a biopsy will generally be required to make a firm diagnosis, and polyps cannot be removed during a CT colonography.
Test kits exist that can be used at home to detect whether there is any blood present in a person’s feces. If this is the case then a person is likely to have some sort of bowel issue, which may be colorectal cancer.
- A fecal occult blood test (FOBT), also known as a guaiac test
- A fecal immunochemical test (FIT)
An immunochemical test is easier to use and is better at detecting abnormalities, but it is generally more expensive than a guaiac test.
If either test gives an abnormal result, i.e. a significant amount of human blood in the feces, then a colonoscopy will be required. A positive result of blood in the feces does not necessarily mean a person has colorectal cancer. There are several other conditions that can cause this symptom, including hemorrhoids and anal fissures.
Stool tests are useful for letting doctors know if a person should have a colonoscopy. However, they are not enough to rule out the presence of colorectal cancer alone and should not replace regular colonoscopy screenings.
Colorectal cancer screening
Colorectal cancer screening is very effective, and all the diagnostic tests described above reduce the risk of developing the disease considerably. There is some debate about what age people should begin being screened and how regularly screening should happen.
The age screening should begin
In the U.S., the current guidelines are that regular screening for colorectal cancer should begin at the age of 50. For those at increased risk of colorectal cancer, e.g. people with a family history of the condition, doctors may recommend that regular screening begins at an earlier age, usually around 45. However, this depends on the condition. For example, people affected by FAP are recommended to begin being tested between the ages of 10 and 12.
The American Cancer Society even argues that regular screening should begin for everyone, not just high risk groups, once they reach 45 and even earlier for people with high risk for colon cancer.
In England, the National Health Service (NHS) recommends regular screening from the age of 55 onwards.  However, NHS England is set to lower that age to 50 in the coming years, bringing it into line with the NHS in fellow U.K. countries Scotland and Wales.
The conversation around these guidelines is continually evolving. It is generally recommended to see a physician for regular health check-ups. In cases of any doubt about symptoms or test results, a proper diagnostic work-up is recommended, even if someone is younger.
How regularly screening should occur
The regularity of testing depends on the test chosen. For example, some people choose to try and avoid more invasive tests, such as a colonoscopy. However, this usually means that they will require testing more regularly. A doctor will be able to advise on the differing testing methods. In the U.S., the guidelines are as follows:
- Colonoscopy testing every 10 years
- Flexible sigmoidoscopy testing every 5 years
- Double-contrast barium enema testing every 5 years
- Computed tomographic (CT) colonography testing every 5 years
A person will only have to undergo one of these types of test at the time intervals listed above, e.g. a sigmoidoscopy at ages 50, 55, 60 and so on. However, a colonoscopy will generally be required if any of the other tests listed above comes back with an abnormal result.
Stool-based FOBT and FIT tests should take place yearly if that route is chosen. FIT tests for DNA do not necessarily have to take place every year, but the gap between tests should be a maximum of three years.
Guidelines differ by country. The NHS in England offers a one-off flexible sigmoidoscopy, known in the U.K. as bowel scope screening, for people aged 55. A stool test is then sent to people aged over 60 to complete every two years. If either of the two above tests produces abnormal results, then a colonoscopy is likely to be recommended.
Colorectal cancer staging
Once colorectal cancer is diagnosed, doctors will try to find out whether it has spread and, if so, how far, in a process known as staging.
The staging system most often used for colorectal cancer is the TNM system, developed by the American Joint Committee on Cancer (AJCC). In the TNM system:
- T refers to tumor size
- N refers to the number and location of lymph nodes with cancer
- M refers to whether the cancer has metastasized or spread
The tumor may also be given a grade, which describes how abnormal the cancer cells look under the microscope and may be factored into the staging.
The cancer may then be given a number stage from 0 to 4, often followed by subdivisions of a, b or c. The lower the number, the less the cancer has spread.
Stage 0 colorectal cancer
This describes when the cancer is at the earliest stage possible and only exists in the mucosa of the bowel. Stage 0 colorectal cancer is also described as carcinoma in situ.
Stage 1 colorectal cancer
The cancer has spread into the submucosa, a layer of tissue that connects the mucosa to the muscular layer of the bowel. Cancer may have also reached the muscular layer at this stage. However, it has not spread to other parts of the body or to the lymph nodes.
Stage 2 colorectal cancer
The cancer has grown and moved to the outer layer of the bowel and potentially:
- Through the muscle wall
- To nearby tissue outside the bowel and potentially nearby organs
The cancer has not spread to distant parts of the body or to the lymph nodes.
Stage 3 colorectal cancer
The cancer has spread to nearby lymph nodes or to the fat that surrounds the lymph nodes, but not to distant parts of the body.
Stage 4 colorectal cancer
The cancer has spread to distant parts of the body, such as the liver or lung.
Treatment of colorectal cancer depends on what stage the condition has reached and where in the large intestine the cancer begins.
Colorectal cancer, particularly in its early stages, may be curable. However, a cure may not be possible in some cases. At that point, treatment will be guided towards either slowing down the growth of the cancer or to easing the symptoms that the cancer is causing.
Treatment for stage 1, 2 and 3 rectal and colon cancers, i.e. before the cancer has spread to other organs or distant sites in the body, will generally all involve surgery. Surgery is the only way to cure colorectal cancer.
Colon cancer surgery
During colon cancer surgery, any cancerous growths in or around the colon will be removed. The surgical removal of part or the entirety of the colon is known as a colectomy. There are two ways the procedure can be done:
- An open colectomy involves making a large incision in the abdomen and removing the cancerous section of the colon
- A laparoscopic colectomy is a less invasive form of surgery. Small incisions are made in the abdomen and a camera guided inside. The surgeon uses the live video feed and surgical tools to bring the colon out through the incision so it can be operated upon outside the body.
Usually, only a part of the colon will be removed. However, for people with colon cancer linked to genetically inherited conditions such as FAP and HNPCC then a total colectomy, in which the entire large intestine is removed, may be required. In either case, a colostomy may be a temporary or permanent requirement.
Rectal cancer surgery
Rectal cancer surgery also requires the removal of cancerous growths. If the cancer is caught very early, then this may be possible to achieve during a colonoscopy. However, in most cases a larger part of the rectum as well as surrounding tissue will need to be removed.
If the cancer is in the upper part of the rectum, it may be possible to remove just a part of the rectum and then reconnect the colon to the lower part. However, if the cancer is in the lower section then the entire rectum and anus may need to be removed through a type of surgery called an abdominoperineal resection. The latter option will require a permanent colostomy.
After rectal or colon cancer surgery, a doctor may need to perform a colostomy. A colostomy is an operation which allows the body’s waste to be diverted out of the large intestine through a hole in the abdomen. Over this hole is a pouch, known as a colostomy bag, in which the waste can be collected. A colostomy may be required:
- If the doctor wants the remaining parts of the bowel to heal before being joined back together. In this case, the colostomy may be temporary.
- If enough of the bowel has been removed that it can no longer control bowel movements, such as when the rectum and anus are removed. In this case, the colostomy is likely to be permanent.
Colostomies cause a considerable amount of change to a person’s life and will take some time to get used to. However, after a period of adaptation, most people can live relatively normal lives.
Metastatic colorectal cancer surgery
The standard treatment for stage 4 colorectal cancer is chemotherapy aimed at managing symptoms rather than curing the disease. However, there are a number of cases where surgery may still be an option if the spread is limited to certain organs, such as the liver or the lung. A doctor will be able to advise on whether this is a possibility.
Chemotherapy and radiotherapy
Chemotherapy is the use of drugs and medication to treat cancer. Radiotherapy is the use of beams of radiation to kill cancer cells. Neither of these treatments can entirely remove colorectal cancer on their own. When they are used alongside surgery in an attempt to rid the body of cancer, chemotherapy and radiotherapy are called adjuvant. If the cancer has spread to the point where surgery is no longer an option, then chemotherapy and radiotherapy may be used to manage symptoms and prolong a person’s life.
Adjuvant chemotherapy and radiotherapy
Chemotherapy is usually administered for three to six months after surgical treatment for cancer in the colon or rectum. The aim of this will be to kill any remaining cancer cells in the body. Post-surgery radiotherapy is usually only used when the cancer is located in the rectum and is generally given alongside chemotherapy.
When the cancer is located in the rectum, then it may be recommended to use a combination of radiotherapy and chemotherapy in advance of surgery. This is known as neoadjuvant chemotherapy and radiotherapy. In some cases, a short course of just radiotherapy may be given ahead of surgery. Neoadjuvant treatment will almost always need more chemotherapy and sometimes more radiotherapy, after surgery has taken place.
In many cases, colorectal cancer can be cured. However, this generally depends upon the stage of the cancer’s development.
The survival rate for those diagnosed with stage 0 or stage 1 colorectal cancer is very high. Screening for colorectal cancer has significantly contributed to a drop in both the number of people being diagnosed with the condition and the number of deaths. Despite these improvements, over a third of U.S. adults aged between 50 and 75 have never been screened for colorectal cancer.
Once colorectal cancer has spread to other parts of the body, it is much harder to treat, which is why regular screening for the condition is so important.
Colorectal cancer survival rates
The National Cancer Institute has produced five-year relative survival rates for different stages of colorectal cancer. This refers to the percentage chance a person diagnosed with that stage of colorectal cancer has of surviving compared to the general population.
This is a more useful statistic than the plain survival rate, as some people with colorectal cancer are likely to have died after five years for unrelated reasons. The relative survival rate factors in this possibility and, as a result, gives a more accurate forecast of the disease’s dangers.
The relative five-year survival rates for cancer located in the colon are as follows:
- 92 percent at stage 1
- Between 65 percent and 87 percent at stage 2
- Between 53 percent and 72 percent at stage 3
- 12 percent at stage 4
The relative five-year survival rates for cancer located in the rectum are as follows:
- 88 percent at stage 1
- Between 50 percent and 81 percent at stage 2
- Between 58 percent and 83 percent at stage 3 -13 percent at stage 4
The large amount of variation at different stages is because of the complexity of the staging system. For example, the cancer may have grown very aggressively in the colon, but not spread to other parts of the body. It is unclear why the relative survival rate was better at stage 3 than stage 2 for rectal cancer.
Q: What is the best way to prevent colorectal cancer?
A: The best way to prevent colorectal cancer is to make sure not to miss regular screening. If a family member has had colorectal cancer in the past or you have been diagnosed with an inflammatory bowel condition such as Crohn’s disease, then ask your doctor for advice on when screening should begin. The following are also thought to lower the risk of the condition:
- Regularly exercising
- Avoiding being overweight
- Stopping using tobacco products
- Eating a diet rich in green and leafy vegetables
- Cutting down on red and processed meats
- Getting lots of good fiber, through foods such as whole-grain bread, oats, barley and rye
Other names for colorectal cancer
- Bowel cancer
- Colon cancer
- Colorectal carcinoma
- Malignant neoplasm of colon
- Rectal cancer
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Lymph nodes filter and break down bacteria or other harmful cells in the body. When they have cancerous cells, this is a sign that the cancer has spread to the lymphatic system, a part of the immune system, from where it may be carried to other parts of the body and may form new tumors. ↩ ↩
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A double-contrast barium enema is a type of X-Ray that can be used to examine the bowel. Even though it is included in screening guidelines, it is not judged to be as effective as similar tests and, as a result, is less likely to be used by doctors. ↩
The mucosa or mucous membrane is a protective layer that lines different cavities inside the body. ↩
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