Colon cancer is a malignancy that begins in the colon, or in the large intestine. The large intestine is an organ which is a long, tube-shaped structure located near the rear end of the digestive system. The colon plays an important role in digestion, since it is responsible for the extraction of some key fluids and nutrients from all consumed food. The colon is also an important unit in the process of excreting solid waste from the human body, via the rectum.

How does colon cancer start developing?

Colon cancer is known to start forming as benign polyps. Benign polyps are either flat, or knob-shaped growths that are present on the inner lining of the large intestine. Occasionally, these growths are known to cause symptoms such as unexplained bleeding (the presence of blood in the stool), or constipation. However, in most cases, these polyps produce no early symptoms at all – which is why most people may not even realize when these signs are present.

Some polyps may continue to remain benign, which means that they will exist as non-cancerous masses. Some of these tumors can become malignant, or cancerous. These polyps are often detected using a procedure called a ‘colonoscopy’. In most cases, if doctors find the presence of one or more polyps during a routine colonoscopy, they are removed at the same procedure.

Colon cancer starts with a growth in the inner lining of the colon. These growths are called polyps. Some types of polyps can change into cancer over time but it depends on the type of polyp it is. Polyps are of two types:

Adenomatous polyps:

These polyps are called adenomas and can sometimes turn to be cancerous.

Hyperplastic polyps and inflammatory polyps:

These polyps are not precancerous.

The factors that can make a polyp cancerous include if the polyp is larger than 1 cm, if two or more polyps are found and if dysplasia is seen after the removal of a polyp. Dysplasia is a precancerous condition which means that there is an area in the polyp that contains cells that look abnormal.

What are the different types of colon cancer?

Adenocarcinomas make up about 96% of the colon cancer cases. These cancers mainly start in the cells that line the inner surface of the colon and these cells are also responsible for lubricating the colon. When doctors speak of colon cancer they are often referring to adenocarcinomas. There are also rarer tumor types which include:

Carcinoid tumors

These tumors start in the hormone-producing cells of the intestine and are most common type neuroendocrine tumors. Most of these kinds of tumors are generally present in the stomach, intestines, colon, liver, and rectum. Carcinoid tumors can take several years to grow and for the same reason, they are classified as low-grade tumors. The most common methods of treatment used for these tumors are surgery, chemotherapy and, hormone therapy.

Gastrointestinal stromal tumors

Gastrointestinal stromal tumors start in cells that are in the wall of the digestive tract. These tumors start in special cells known as interstitial cells of the Cajal (ICCs). These cells are a part of the autonomic nervous system and send messages to muscles in the gastrointestinal tract to contract to move food and liquid along.
Gastrointestinal stromal tumors can start anywhere along the gastrointestinal tract but a very small number grow outside of the gastrointestinal tract. Gastrointestinal stromal tumors can grow and spread to other parts of the body too and doctors look into a number of factors to tell if the tumor is likely to grow and spread.

Lymphomas

Lymphomas are cancer cells that are found in the lymph nodes and can grow and start anywhere including areas like the colon or other organs.

Sarcomas

These cancers can start in the blood vessels, connective tissues and muscle layers in the walls of the colon. However, sarcomas of the colon are rare.

Most people who have colon cancer at the early stages show no symptoms. When the symptoms show, they will vary based on the size of the tumor, the location and how far the cancer has spread. The most common symptoms of colon cancer are:

• Easy fatigability
• Change in bowel movements like constipation or diarrhea
• Blood in stools which may appear like black tarry stools or bright red colour
• Pain abdomen
• Weight loss
• Persistent abdominal discomfort like cramps or gas
• A bowel movement that does not let one feel relieved
• Rectal bleeding which is bright red

A risk factor is known as a factor that increases a person’s chance of developing cancer. Risk factors often influence the development of cancer but don’t directly cause it. If you have a few risk factors it is better to speak to your doctor about it so that health and lifestyle changes can be made and prevention of colon cancer can be taken care of.

In most cases, colon cancer is considered sporadic, which means that genetic changes occur in a person’s body after they are born. Inherited colon cancers are less common and are seen only in 5% of the cases and they occur when gene mutations or changes are passed down within a family from one generation to the next. The actual cause of colon cancer is unknown, however the following factors may increase the risk of developing colon cancer

Age

Age is an important risk factor, as colon cancer can affect teenagers and young adults too but majority of colon cancer cases occur after the age of 50. For colon cancer, the average age at the time of diagnosis for men is 68 and for for women is 72. Older patients who are diagnosed with colon cancer do face some issues in terms of cancer treatment.

Family history of colon cancer

If a person has a family history of colon cancer, it doubles the risk of developing it. Colon cancer may run in the family with first degree relatives like parents, sister, brother etc. and even with other relatives like grandparents, uncles, nieces, nephews etc. The risk increases furthermore if a first degree relative has been diagnosed at a younger age with colon cancer. If you have known of family members who have had colon cancer, it is best to speak to a genetic counsellor and get genetic testing done as it can determine if a gene mutation is present.

Rare inherited conditions

People in families that have rare inherited conditions are at a higher risk of developing colon cancer. These rare inherited conditions include lynch syndrome and familial adenomatous polyposis. Lynch syndrome increases the chance developing colon cancer and other cancers. Familial adenomatous polyposis is a condition that causes a person to develop thousands of polyps in the lining of the colon. People untreated with familial adenomatous polyposis are at an increased risk of developing colon cancer before the age of 40.

Inflammatory Bowel Syndrome (IBS)

People who have inflammatory Bowel Syndrome (IBS) may develop chronic inflammation of the large intestine which can increase the risk of colon cancer.

Adenomas

Adenomas are otherwise also known as adenomatous polyps which are non-cancerous growths that develop in the colon. These growths can be removed during a colonoscopy if they are identified. People who have adenomas are always at a higher risk of developing colon cancer.

Physical inactivity and obesity

People who live an inactive lifestyle are at a higher risk of developing colon cancer. Being inactive means not having proper exercise and this can in turn lead to obesity. People who are obese have weight on the midsection and an increased waistline which puts them at a increased risk of developing colon cancer.

Diet

Recent studies show the kind of diet that a person has plays an important role too. Eating a lot of read meat and processed food can put people at a higher risk of developing colon cancer. The recommended diet for people who are at high risk is a low-fat high-fiber diet which has a lot of fruits and vegetables and very little of meat and processed food.

After diagnosis, one of the most important procedures done next is staging. Staging refers to gauging extent of the cancer and how far it has spread. Colon cancer staging is very important as it can help doctors determine the kind if treatment that is required.

The colon cancer staging is done based on the TNM system of staging.

The TNM system of staging has the following factors:

Tumor (T): This factor refers to how far the cancer has grown into the wall of the colon. These layers include, the mucosa which is the inner lining, the sub-mucosa which is the fibrous tissue below the muscle, the muscularis propria which is a thick muscle layer and the serosa which is outermost covering layer

Lymph node s (N): This factor indicates if the cancer has spread to the lymph nodes.

Metastasis (M): This factor refers to whether the cancer has spread to other parts of the body.

Classification of colon cancer stages

Within each stage, the cancer is classified and given a number or letter that indicates the extent of the disease. These numbers and letters are given based on how far the cancer has spread.

Stage 0 (Tis N0 M0) Colon Cancer and its Treatment

This is the earliest stage of colon cancer and it also means that the cancer has not grown beyond the mucosa or the innermost layer of the colon

There are different treatments used in colon cancer but most of the treatment depends on the extent of the cancer and many other factors. People who have colon cancer that has not spread usually have surgery as the first or main treatment and later chemotherapy is given.

For the treatment of stage 0 colon cancer, surgery is the only kind of treatment that is used as in stage 0 the cancer is in its initial stages and has not grown beyond the inner lining of the colon. For the treatment of stage 0 colon cancer there are two kinds of surgery that are used, a local excision and a segmental colectomy. In the procedure of a local excision, the polyp is removed or the area containing the cancer is taken out with a colonoscope. A part the colon is removed in the procedure of a segemental colectomy. This is usually done if the tumor is too big to be removed in a local excision.

Stage 1 Colon Cancer and its Treatment

At this stage, it means the cancer has grown into the mucosa and submucosa. In stage 1 colon cancer, the cancer has grown deeper into the colon wall but has not spread to the nearby organs or lymph nodes. Stage 1 colon cancer also includes cancer that was a part of the polyp. If the part of the polyp that contained the cancer was removed during a colonoscopy, with no cancer cells at the margins of the removed piece, no other treatment may be required. However, if the cancer found on in the polyp is of a higher grade or if cancer found at the margins of the polyp, more surgery may be required.

The patient may also be advised to have more surgery if the polyp could not be completely removed or if the polyp had to be removed in bits and pieces making it hard to see if there were cancer cells at the edges.

A partial colectomy is done for cancers that are not in the polyp. A partial colectomy is the process of removing a part of the colon that has cancer and even the nearby lymph nodes. This is the standard treatment for stage 1 colon cancer and the patient won’t need anymore treatment after this.

Prognosis of stage 1 colon cancer

The 5 year relative survival rate of people with stage 1 colon cancer is about 92%.

Stage 2 Colon Cancer and its Treatment

In this stage, the cancer is a little more advanced than stage 1 and has grown beyond the mucosa and submucosa. Stage 2 can further be classified into stage 2A, 2B or 2C. Stage 2 colon cancers have grown into the wall of the colon and nearby tissue but has not spread to the lymph nodes.

Surgery is the primary treatment for stage 2 colon cancer. A partial colectomy is conducted which is the removal of a part of colon that contains cancer. Sometimes even the nearby lymph nodes are removed. The doctor might also recommend adjuvant chemotherapy, which is chemotherapy that is given after surgery. The doctor recommends this to patients who are at higher risk of the cancer coming back. The risk of the cancer coming back has certain factors involved and they include:

• The cancer looked high grade or abnormal when viewed under a microscope
• Cancer has grown nearby lymph or blood vessels
• The surgeon has not removed at least 12 lymph nodes
• Cancer was found in or near the margin of the removed tissue
• The cancer had obstructed the colon
• The cancer caused a hole in the wall of the colon

Chemotherapy may be used in combination. It’s important to discuss the pros and cons of chemotherapy with the doctor including how much the risk of cancer recurring is lowered by receiving chemotherapy.

Prognosis of stage 2 colon cancer

For people with stage 2A colon cancer the relative survival rate is 87% and for people with stage 2B colon cancer the relative survival rate is 65%.

Stage 3 Colon Cancer and its Treatment

Stage 3 is further classified into 3A, 3B and 3C, the difference between these classifications further depends on how far the cancer has spread and the affected lymph nodes. Stage 3 colon cancers have spread to the nearby lymph nodes but has not yet spread to the distant organs.

A partial colectomy is the kind of surgery that is conduct for people with stage 3 colon cancer. A partial colectomy is the procedure where in a part of the colon that had been affected by cancer is removed. After the surgery the standard treatment option is adjuvant chemotherapy. Adjuvant chemotherapy is chemotherapy that is given after surgery.

Radiation therapy or chemotherapy may also be used as treatment options for people who are not in good health for surgery. The radiation therapy may be given after surgery to prevent the recurrence of cancer. It may also be given if the tumor has grown into the nearby tissue or if it has attached itself to the nearby tissue. It may also be given in cases where cancer could not be fully removed.

Chemotherapy is also given after surgery to reduce the risk of recurrence. Chemotherapy is started 4 to 6 weeks after surgery and is given for 6 months.

Prognosis of stage 3 colon cancer

People with stage 3A colon cancer have a five year relative survival rate of 90%. People with stage 3B have a five year relative survival rate of 72% and people with stage 3C of colon cancers have a five-year relative survival rate of 53%.

Stage 4 Colon Cancer and its Treatment

Stage 4 colon cancer is considered to be the most advanced stage as the cancer may have spread to one distant site like the liver or lungs. This stage is also further divided into stage 4A and 4B. Stage 4 colon cancers have spread from the colon to distant organs like the liver. The cancer can also spread to the lungs, brain and the lining of the abdominal cavity which is known as the peritoneum.

In the case of stage 4 colon cancer conducting surgery is very unlikely. In cases where there are only a few areas where the cancer has spread to the liver or lungs surgery maybe done. Surgery can make a person live longer and may even cure the person. During surgery, the section of the colon that has been affected by cancer is removed along with the nearby lymph nodes and other areas to which the cancer has spread to.

Chemotherapy is given before surgery and or after surgery. Sometimes,hepatic artery infusion is given when the cancer has spread to the liver. A hepatic artery infusion is a procedure where in chemo is given directly into the hepatic artery.

If the tumors cannot be removed because they are too big, Chemotherapy might be given before surgery and the tumor shrinks,then surgery may be conducted to remove the tumor. Sometimes surgery might also be needed if the tumor is blocking the colon. Surgery in this case can also be avoided by putting a stent, which is hollow metal or plastic tube into the colon during a colonoscopy. If not, operations such as a colostomy may be used.

Read more on what is colon cancer here.

Doctors use different tests to diagnose cancer and some of these tests may include imaging tests and blood tests. These kinds of tests are also done to find out if the cancer has spread from where it had started. For diagnosing a type of cancer there are various factors that are looked into like, the suspected cancer, the patients signs and symptoms, the patient’s health and medical condition, medical and family history and lastly, results from previous medical tests.

In addition to a physical exam, the following tests may be done to diagnose colon cancer.

Colonoscopy

A colonoscopy is done when a patient is sedated. It allows the doctor to look into the patients colon and also to take a sample of tissue for the confirmation of cancer. If colon cancer is found, an accurate diagnosis with the location is given by the doctor.

Molecular testing of the tumor

Laboratory tests are run on the tumor sample to check for specific genes, proteins and any other factor that might be unique to the tumor. If the person has metastatic colon cancer, a sample of the tissue from the area that it has spread too might be taken for testing. This will decide if treatment options include targeted therapy.

Biopsy

A biopsy is the removal of a small amount of tissue that is then examined under a microscope. A biopsy can also be seen as a definite diagnosis to see if colon cancer is present. In a biopsy, a pathologist will analyze the sample which includes evaluating cells, organs, and tissues to make a diagnosis. A biopsy can be done during a surgery or colonoscopy. A CT scan or ultrasound is used to perform a needle biopsy.

Blood tests

A blood test to check for the complete blood count of a person is done to check for anemia. If a person has anemia, which is low red blood cell count, it means the tumor has been bleeding for a long time. A blood test may also be done to check for liver function as colon cancer can spread to the liver as well.

Computed Tomography (CT) scan

A CT scan can be used to check if colon cancer has spread to the liver. In a CT scan, X-rays are used to make detailed cross sectional images of organs.

PET CT SCAN

Sometimes pet-ct scan is needed to look for any distant spread from the colon cancer.Radionuclide material is used in this scan.

CEA

It is blood investigation helps in detecting and monitoring for recurrence in colon cancer. It is tumor marker. However, not all colonic cancer patients may not have raised serum cea values. In smokers also it is slightly elevated compared to non smokers.

Gene tests

Gene tests are often conducted to check to check for specific gene changes in cancer cells. This test is usually done to check how treatment might affect these cells in cases where the cancer has spread. Colon cancer cells are typically tested to check for high levels of gene changes called microsatellite instability (MSI). Testing is also done to check if the cancer cells show changes in any of the mismatch repair genes (MLH1, MSH2, MSH6 and PMS2)

Treatment options for colon cancer depends on several factors like stage of the cancer, type possible side effects and the patients overall health. There are several kinds of treatment that are used for colon cancer and they include:

Surgery for colon cancer

This is the most common treatment for colon cancer and is called a surgical resection. In this procedure along with the affected part, part of the healthy colon or rectum and lymph nodes will be removed. Read more about Colon cancer surgery here.
surgery is done by either of the three methods

1. open method
2. laparoscopic method
3. robotic method

Other than a surgical resection, there are many other surgical options for colon cancer and they include:

Open Method

In this traditional method, long cut is made vertically on the skin in the midline and along with the affected part, part of the healthy colon and lymph nodes will be removed. Usually it takes 7 to 8 days of hospital stay.

Laparoscopic surgery

In this technique several viewing scopes are passed into the abdomen. The incisions made are small and recovery time is shorter than a standard colon surgery.

Robotic method

in this similar to the laparoscopic method incisions are small and instruments (robotic arms) are inserted and the surgeon operates at the console which controls the robotic arms.

Chemotherapy for colon cancer

Chemotherapy is the use of cytotoxic or anticancer drugs to kill cancer cells. The most common ways used to give chemotherapy include the intravenous method where the tube is placed into the vein using a needle or the chemotherapy drugs can be taken orally by the patient. Chemotherapy may be given after surgery to kill any remaining cancer cells. Read more about side effects of chemotherapy for colon cancer here.

Targeted therapy

Targeted therapy is the kind of therapy that targets cancer cells including specific genes, proteins or even the tissue environment that contributes to the growth of cancer cells. This type of treatment blocks the growth and spread of cancer cells while limiting the damage that is done to healthy cells. There are different types of targeted therapies which that are used, they include:

Anti-angiogenesis therapy

A kind of targeted therapy that focuses on stopping angiogenesis, which is the process of making new blood cells. The tumor needs nutrients from the blood cells to survive and the goal of anti-angiogenesis therapy is to starve the tumor.

Epidermal growth factor receptor (EGFR) inhibitors

An EGFR inhibitor is a kind of targeted therapy and studies have found that blocking the epidermal growth factor receptor may be beneficial for blocking or slowing down the growth of colon cancer.

Checkpoint Inhibitors

Also known as immunotherapy. Immunotherapy is a way of boosting the defenses of the body to fight cancer.

Radiation therapy for colon cancer

Radiofrequency ablation (RFA) or cryoablation

These procedures are used for the liver metastasis. In the procedure of a radiofrequency ablation, high energy radio waves are used to kill tumors. A CT scan or ultrasound is used to guide a needle like instrument through the skin and into the tumor. An electric current is passed to the tip of the instrument, releasing high frequency radio waves that heat the tumor and kill the cells. A cryoablation is a procedure that uses extreme cold to destroy a diseased tissue. The procedure is performed using hollow needles through which cooled thermally conductive fluids are circulated. The cryoprobes are positioned adjacent to the target in such a way that the freezing process will destroy the affected tissue. Read more about side effects of radiation therapy for colon cancer here.

How To Prevent Colon Cancer?