What is colorectal cancer?

Colorectal cancer, also known as colon, rectal or bowel cancer, occurs when abnormal cells grow uncontrollably in the intestines and/or the rectum. A major cause of preventable death in adults, colorectal cancer usually takes many years to develop and may often have no initial symptoms.

Screening tests are available that can help to identify colorectall cancer at an early stage. Screening is the process of looking for cancer in people who have no symptoms. Several tests can be used to screen for colorectal cancers. These tests can be divided into:

  • Tests that can find both colorectal polyps and cancer - These tests look at the structure of the colon itself to find any abnormal areas. This is done either with a scope (a tube-like instrument with a light and camera) put into the rectum or with special imaging (x-ray) tests. Polyps found during these tests can be removed before they become cancer, so these tests may prevent colorectal cancer. Because of this, these tests are encouraged if they are available and you are willing to have them.
  • Tests that mainly find cancer - These tests check the stool (feces) for signs of cancer. These tests are less invasive and easier to have done, but they are less likely to detect polyps.

Tests that can find both colorectal polyps and cancer are encouraged if they are available and you are willing to have them. But the most important thing is to get tested, no matter which test you choose.

These tests, as well as others, can also be used when people have symptoms of colorectal cancer and other digestive diseases such as inflammatory bowel disease.

Cells

The fundamental unit of life; the simplest living unit that can exist, grow, and reproduce independently. The human body is composed of trillions of cells of many kinds.

Polyps

A small growth that protrudes from a mucous membrane.

Rectum

The final part of the large intestine, leading to the anus.

Causes

The cause of colorectal cancer, as with other cancers, is due to damage to cellular DNA. This damage results in uncontrolled growth of abnormal cells, which leads to the formation of a tumor. In colorectal cancer, the tumor commonly starts as a benign lesion (i.e., it does not invade beyond its normal boundary). This benign tumor is commonly referred to as a polyp, which can be seen at the time of a colonoscopy  as a pink growth that protrudes into the inside of the bowel. This polyp can continue to grow and invade deeper tissues, at which point it becomes a malignant tumor - cancer - and can spread (metastasize) throughout the body via the bloodstream or lymphatic system.

Bloodstream

The flow of blood within the blood vessels of the circulatory system.

Cells

The fundamental unit of life; the simplest living unit that can exist, grow, and reproduce independently. The human body is composed of trillions of cells of many kinds.

Colonoscopy

A medical procedure that uses a colonoscope to examine the large bowel.

DNA

The genetic material of all living cells and some viruses. The full name is deoxyribonucleic acid.

Lymphatic system

A network of vessels, lymph nodes, the spleen and other organs that transport lymph fluid between tissues and bloodstream.

Tumor

A growth caused by an abnormal and uncontrolled reproduction of cells.

Risk factors

Risk factors for colorectal cancer include:

  • Age - colorectal cancer is more common for those aged 50 years and older;
  • Genetics and family history - having a family history of colorectal cancer increases your risk. Particular genetic disorders, such as familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), can markedly increase your risk of colorectal and certain other cancers;
  • Ulcerative colitis - this is a condition that results in an inflamed colon. The longer that someone has ulcerative colitis, the greater the risk that the damage caused by inflammation can develop into cancer, and;
  • Lifestyle - a diet high in processed or red meat, and health hazards such as smoking, alcohol abuse and obesity may increase the risk of developing colorectal cancer.

Genetics

Related to genes, the body's units of inheritance or origin.

Familial adenomatous polyposis

An inherited condition, caused by a faulty gene, which leads to multiple polyps in the bowel that invariably develop into bowel cancer by a young age.

Types

Adenocarcinomas

These cancers originate in the glands that produce mucus in the colon. They account for the vast majority of colorectal cancer cases.

Carcinoid tumor

These tumors originate in the hormone-producing cells of the colon. This is a very rare type of cancer.

Gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) originate in special cells of the gastrointestinal tract called 'interstitial cells of Cajal'. They can be either benign or malignant. 

Lymphoma

This type of cancer usually originates in the lymph nodes, such as in the neck and groin, from abnormal immune cells. However, there is also lymph tissue within the gastrointestinal tract, where lymphomas can also occur. 

Sarcoma

These tumors can originate in the muscle, blood vessels, or connective tissue lining the wall of the colon.

Cells

The fundamental unit of life; the simplest living unit that can exist, grow, and reproduce independently. The human body is composed of trillions of cells of many kinds.

Gastrointestinal tract

The membrane-lined series of organs extending from the mouth to the anus through which food passes during digestion.

Interstitial cells of Cajal

Cells in the gastrointestinal tract that play an important role in the rhythmic contraction of gut muscles during digestion.

Stages of colorectal cancer

Treatment outcomes can vary greatly depending on the stage of cancer. Cancer is staged according to the size and location of the primary tumor and whether it has spread to lymph nodes or organs throughout the body.

Stage I

The cancer has spread beyond the mucosa into the submucosa or muscle wall.

Stage II

The cancer has spread beyond the bowel wall through its outer surface, the serosa.

Stage III

The cancer has spread to the lymph nodes near the bowel.

Stage IV

The cancer has spread throughout the body to distant organs, often initially involving the liver.

Stages of colon cancer.Four stages of colorectal cancer. 

Tumor

A growth caused by an abnormal and uncontrolled reproduction of cells.

Mucosa

The lining of the walls of organs such as the stomach, intestines, nose and mouth.

Signs and symptoms

In the early stages of colorectal cancer, there are commonly no symptoms. As a result, some countries have introduced colorectal cancer screening programs, which help to identify people at risk of developing colorectal cancer before they develop any symptoms.

The symptoms of colorectal cancer typically develop as the tumor enlarges and/or becomes cancerous. These symptoms include:

  • Blood or mucus in the feces;
  • Changes in bowel movements such as constipation or diarrhea;
  • Fatigue, weakness and paleness, and;
  • Discomfort in the abdomen.

Occasionally, colorectal cancer may only be diagnosed once it starts to cause complications (see below), such as iron-deficiency anemiabowel obstruction and/or as a result of metastatic disease. 

Tumor

A growth caused by an abnormal and uncontrolled reproduction of cells.

Methods for diagnosis

To identify your risk of having colorectal cancer, your doctor will take a thorough medical history and perform a physical exam, which includes a digital rectal exam (DRE). During the DRE, your doctor will insert a lubricated gloved finger into your rectum to feel for any lumps or swelling.

Blood test

A blood test may detect iron deficiency anemia, which can be a common finding in colorectal cancer as a result of hidden (occult) bleeding. Some cancer cells produce a substance called carcinoembryonic antigen (CEA). A high level of CEA in a blood test can indicate the presence of cancer, but it can also occur in people who do not have cancer, including smokers and during pregnancy. CEA is more often used in monitoring the efficacy of treatment and/or ongoing follow-up. Similarly, other markers can be used in the diagnosis and management of carcinoid tumors.

Procedures

Sigmoidoscopy

This procedure involves the insertion of a thin, flexible lit tube called a sigmoidoscope into the bowel through the anus. It allows your doctor to see the lower part of the colon and rectum. A biopsy can also be taken during this procedure if needed. A sigmoidoscopy is a very brief procedure that can be conducted in a clinic without the need for an anesthetic or sedation.

Colonoscopy

A colonoscopy is used to examine the entire length of the colon. Before the procedure, the bowel may need to be cleansed using an oral laxative solution or an enema. You may also be asked to not eat, but to drink plenty of clear fluids in the 12-24 hours prior to the procedure. During the colonoscopy a thin, flexible tube with a camera is passed through the bowel, via the anus. Air is usually pumped through the bowel to allow your doctor to properly view the inside lining for polyps and other lesions.

Scans

A range of scans may be used to aid diagnosis, including:

  • A computerized tomography (CT) scan, which uses X-rays to develop a 3D image of the body. This is the most commonly used initial scan to help to diagnose the metastasis of colorectal cancer. It can also assess for spread of cancer (metastasis) to other areas or organs;
  • Ultrasound - your doctor may perform an abdominal ultrasound or endorectal ultrasound. During the abdominal ultrasound you'll lay down on a bed and a hand-held device will be rubbed over your abdominal area. This may be performed to give a good view of the liver, which is usually the first site of metastasis of colorectal cancer. During an endorectal ultrasound, the doctor will insert this device through the anus into the rectum. This is commonly done under anesthesia, and it may indicate the depth of invasion of a rectal cancer or lesion;
  • Magnetic resonance imaging (MRI) - which is similar to the CT scan, but uses magnetism instead of X-rays. This may be used to better assess rectal cancers;
  • Positron emission tomography (PET) - during which an injection of a radioactive label (tracer) is administered. When combined with a CT scan, it produces a 3D image that helps to identify and locate tumors and any metastasized cancers, and;
  • Nuclear medicine scan - a 2D scan that use the injection of specific radioactive labels to detect carcinoid tumors.  

Biopsy

To conclusively diagnose colorectal cancer and identify its type, a biopsy of the suspected lesion is commonly performed. This is often done at the time of colonoscopy or sigmoidoscopy, if it is easily accessible. Occasionally, a laparoscopy may be performed to obtain a sample of tissue, particularly if it is difficult to obtain using the above procedures. Also, a biopsy may be taken from other sites, if metastasis is suspected. This may be performed by a radiologist using a CT or ultrasound scan to guide a biopsy needle (known as radiologically guided biopsy). The biopsies are sent to a laboratory to be viewed under a microscope for the formal diagnosis.    

Cells

The fundamental unit of life; the simplest living unit that can exist, grow, and reproduce independently. The human body is composed of trillions of cells of many kinds.

Colonoscopy

A medical procedure that uses a colonoscope to examine the large bowel.

Enema

A procedure in which fluid or gas is injected into the rectum for cleansing, diagnostic or therapeutic purposes.

Laxative

Any substance that causes or encourages bowel movements.

Polyps

A small growth that protrudes from a mucous membrane.

Rectum

The final part of the large intestine, leading to the anus.

Laparoscopy

A surgical procedure that uses small incisions through which thin instruments and a slender camera are passed to view and perform surgery on internal organs in the abdomen and pelvis. Laparoscopy offers the benefit of less pain, shorter recovery and smaller incisions compared to conventional surgery, which uses larger incisions. Also known as keyhole surgery.

Types of treatment

Surgery

Surgery is the most common form of treatment for colorectal cancer. Surgical procedures depend on the size and location of the cancer. These may include: 

  • Right or left hemicolectomy - removal of the right or left side of the colon;
  • Transverse colectomy - removal of the middle part of the colon;
  • Sigmoid colectomy - removal of the sigmoid colon;
  • Total or sub-total colectomy - removal of all or nearly all of the bowel;
  • Proctocolectomy - removal of all of the colon and rectum;
  • Abdominoperineal resection or excision - removal of the sigmoid colon, rectum and anus. An artificial opening (stoma) will be made from the end of the descending colon and this will be the opening from which waste is removed;
  • High anterior resection - removal of the lower section of the colon and higher section of the rectum and re-joining the end of the bowel to the rectum, and;
  • Ultra low anterior resection - removal of the lower left section of the colon and all of the rectum and re-joining the end of the bowel to the lower part of the rectum just above the anal canal.

These procedures are generally performed under general anesthetic and can be done using laparoscopy, open surgery or a combination. Often recovery can take up to several weeks in hospital. You will be given pain-relief medications, and often gradually restarted on a normal diet.  

Depending on the procedure and other factors, your surgeon may elect to reconnect your bowel and/or provide you with a stoma. A stoma is where the bowel is brought up to the abdominal wall to allow feces to collect into a bag (stoma bag). This may be a temporary measure to allow your bowel to heal in the months after an operation, or - rarely - it may be a permanent solution. Prior to your operation, your surgeon will often discuss with you if there is a likelihood you'll need a stoma.  

Living with a stoma

Managing a stoma can often be difficult and take time to accept. You may worry about how it will affect your lifestyle and sexuality. Your doctor or a stomal nurse can provide you with the necessary support and help explain how to care for your stoma. They may also recommend some ongoing support services. 

Types of colon cancer surgery.Various surgical procedures for treating colorectal cancer. 

Additional therapies

Other therapies can be used in addition to surgical treatments, to further improve treatment outcomes. They may be given before surgery (neoadjuvant therapy) and/or after surgery (adjuvant therapy). When given before surgery, they aim to reduce the size, and therefore stage, of the cancer. When given after surgery, they aim to help prevent the cancer returning. These non-surgical treatments include chemotherapy, radiotherapy, hormone therapy or a combination of these. 

Occasionally, these therapies may be used if individuals are not suitable for surgical treatment. Often, in these situations, the aim of treatment is to control symptoms, and not necessarily for cure. The treatment options and aims can differ based upon the individual, the stage and type of cancer. Your doctor can help explain this information in more detail. 

Chemotherapy

Chemotherapy works by damaging cancer cells and stopping their reproduction. Various medications can be used, which can be administered intravenously or orally. They are often given in cycles, with intervening rest periods, to help reduce toxic side effects. These side effects include:

  • Nausea, vomiting and fatigue;
  • Altered bowel habits, such as constipation or diarrhea;
  • Joint and muscle pain;
  • Temporary hair loss from the head and body, and;
  • Tingling in the hands and feet - some chemotherapeutic agents can affect the nerves. It is important to tell your doctor if you develop these symptoms. 

Side effects occur because chemotherapy can also affect healthy cells. Your doctor will monitor your dosage carefully to achieve an optimum therapeutic effect.

Radiotherapy

There are various types of radiotherapy. In one type, focused X-rays from an external beam radiation source are applied to the area where the tumor is located. This type of radiotherapy is often used prior to surgery to shrink the size of tumor, which makes the surgery easier to perform. Endocavity radiation involves passing a small device through the anus and into the rectum to administer a short burst of high-dose radiation. This treatment is repeated several times over a couple of weeks and has the benefit of not affecting other tissues, as occurs during external beam radiotherapy. Another form of radiation therapy is brachytherapy, which involves implanting radioactive seeds in the tumor or in the nearby area. This is mainly used to treat rectal cancer and is generally used in people with health conditions that prevent them from having surgery.

Hormone therapy

Carcinoid tumors are a rare type of colorectal cancer that originate in hormone-producing cells. Hormone therapy can inhibit the release of growth hormones that support the growth of these tumors. 

Other therapies

Some people diagnosed with cancer seek out complementary and alternative therapies. None of these therapies are proven to cure cancer, but some can help people feel better when used together with conventional medical treatment. It is important to discuss any additional treatments with your doctor before starting them.

Cells

The fundamental unit of life; the simplest living unit that can exist, grow, and reproduce independently. The human body is composed of trillions of cells of many kinds.

General anesthetic

An anesthetic given to a person to put them to sleep while having an operation or medical procedure. Afterwards, the person regains consciousness and usually has no memory of the procedure. A general anesthetic is given in hospital by a specialist called an anesthetist.

Rectum

The final part of the large intestine, leading to the anus.

Sigmoid

The part of the large intestine before the rectum.

Tumor

A growth caused by an abnormal and uncontrolled reproduction of cells.

Laparoscopy

A surgical procedure that uses small incisions through which thin instruments and a slender camera are passed to view and perform surgery on internal organs in the abdomen and pelvis. Laparoscopy offers the benefit of less pain, shorter recovery and smaller incisions compared to conventional surgery, which uses larger incisions. Also known as keyhole surgery.

Potential complications

Bowel obstruction

Bowel cancers have the potential, if left untreated or diagnosed late, to cause a blockage of the bowel, which is known as a bowel obstruction. This is a serious condition and warrants prompt medical attention. It can present with severe abdominal pain, nausea and vomiting, distension and constipation.  

Recurrence

Cancers can return despite treatment. This is why your doctor will continue to review you at periodic intervals, usually for the first five years. The risk of the cancer returning depends on the initial stage of cancer, the successful removal of the cancer and its response to treatment.    

Metastasis

Colorectal cancer has the potential to spread to other sites. It initially spreads to the liver, but other common sites include the lungs, brain and bone. Previously, metastasis of colorectal cancer was deemed incurable; however, advances in treatments have meant that certain cases can be successfully treated, if not controlled. 

Future colorectal cancers

Once a person develops colorectal cancer, there is often a lifetime risk of further new colorectal cancers. It is important to have lifelong reviews with your doctor to detect any new cancers. 

Prognosis

The prognosis will vary according to the type and stage of the cancer and the way you respond to treatment. 

It is important to remember survival rates are only an indication, and are based upon the averages of previously treated patients. It is not an absolute prognosis for an individual. It is often difficult to accurately predict an individual's cure or survival rate. Constant advances in treatment are continually improving these statistics. 

Prevention

You can reduce your risk of developing colorectal cancer by quitting smoking, reducing alcohol intake and following a healthy diet that is high in fruit and vegetables and low in red and processed meats. colorectal cancer screening programs are available in some countries for people from the age of 50 to help detect colorectal cancers early. If you have a family history of colorectal cancer you may be screened earlier, at routine intervals, usually using colonoscopy.

If you developed a colorectal cancer at the age of 50 or younger, it is important to encourage your immediate family members to get screening from an early age, as their risk is higher. 

Colonoscopy

A medical procedure that uses a colonoscope to examine the large bowel.