Let us briefly understand what colon is and its functions. Digestion of food starts from chewing it in the mouth and ends with excretion of waste from rectum & anus. Once the swallowed food reaches the stomach, it is broken down into smaller particles that then pass into the small intestines. In the small intestines, the vitamins, minerals, energy, water etc are absorbed and the remaining waste matter is sent into the large intestine.
Digestion doesn’t end there; the large intestine again absorbs the water, left over vitamins etc from the waste and then pushes it out of the body. Onto the right side of the body, the large intestine is called ‘ascending colon’, this is typically larger in size. The horizontal part of the large intestine is called is the ‘transverse colon’ and the part of large intestine that is on the left side of the body is called ‘descending colon’. That’s the path taken by the waste matter in the body to travel and exit the body. The left side of the colon is relatively smaller (in width you can say) than the right side of the colon.
Colon is made up of four layers – Inner layer of the colon is called the mucosa. The layer next to the mucosa is called the submucosa and the third layer is called the muscularis as it is the muscular part of the colon. The outermost layer is called the serosa. The most common types of colon cancer (called adenocarcinoma) start in the innermost layer, mucosa and then it spreads into the inner layers of the colon and spreads to other parts of the body.
How cancer develops & spreads inside the colon?
The waste matter that enters the colon contains acids, waste matter generated by digesting food, water, bacteria (from the food and from the smaller intestines) etc. This waste travels through the colon and gets out of the body. During the travel, many cells on the mucosa layer die and get replaced by the body. This is pretty normal. But, in some people, the cells that get replaced are malformed. That can be due to an error in their chromosomes or other reasons. They tend to multiply without any limit (unlike healthy cells) and produce more malformed cells that start as polyps and then into cancerous tumour. Polyps are small structures that are formed with few malfunctioning cells. These are precancerous in nature. As the time passes, more malfunctioning cells build up resulting in formation of cancer tumours. Polyps and cancerous tumours may be confined in a small area or they may have spread throughout the colon in hundreds of numbers.
Once the cancer cells start growing in an area, two things can happen. In the beginning stages, these cells penetrate through the inner layers of the colon. They will also spread to the other nearest organs inside the body. Next stage is that the cancer cells enter the lymph system. Thousands of cancer cells enter the lymph system, gets transported to other parts of the body, typically liver, lungs etc. They then get deposited on those organs and start to multiply and result in formation of tumours. Most typically, the cancer from colon spreads to the lungs and that’s the reason why PET scans or CT scans are performed to detect the spread of cancer to other organs inside the body. This stage is called ‘metastasis’.
Causes and risk factors of Colon cancer
In fact, the exact reason for occurrence of any cancer in human body is yet to be found. Medical researchers and experts are only able to figure out the risk factors that can lead to the formation of cancer cells in the body.
- Age – 90% of colorectal cancer occurs in people above the age of 50 years.
- Race – It was found that more African Americans are diagnosed with Colon cancer than any other race.
- Diet – Consuming foods that contain high amounts of fats. During the digestion of fats in the small and large intestines, it promotes the growth of cancer causing agents. These agents alter the genetic structure of the normal cells and make them malfunction. The malfunctioning cells multiply and lead to cancerous tumours. It was also found that, people who eat less fatty foods and include more of vegetables and fruits in their diet are less prone to develop colon cancer because, the biological chemicals present in vegetables and fruits fight off the cancer causing agents there by reducing the chances of developing cancer cells.
- Colon Polyps – These are local areas formed due to the growth of malfunctioning cells. They are initially non cancerous. But as the time passes and more and more malfunctioning cells grow, the polyps turn into cancer tumours and start spreading, which is the typical nature of cancer.
- Ulcerative Colitis – Ulcerative colitis causes inflammation of the inner lining of the colon. Depending on the location of Ulcerative colitis, the risk of developing colon cancer increases/decreases.
- Genetics – Genetics also play an important role in a person’s body to develop colon cancer. If any immediate family member has been diagnosed with colon cancer, the person may also be at higher risk of developing the same sooner or later. However, in 80% of the cases that are diagnosed with colon cancer, none of their immediate family member was diagnosed with colon cancer.
Symptoms of Colon Cancer
Symptoms of colon cancer vary (in symptoms and time) depending on the location of the cancer tumour. As said earlier, right side (ascending) colon is larger than the left side one (descending colon). When the cancer develops in the right colon, it slowly starts to bleed and the person loses blood resulting in anemia. Anemia will lead to fatigue, weakness and shortness of breath.
If the cancer develops in the left colon, due to the already narrow colon, the waste/stool inside it finds it hard to exit the body, resulting in constipation and related symptoms. This will also cause abdominal pain, diarrhoea, cramps, bloating etc. Redness in stool indicates presence of tumour at the end of left colon or in the rectum.
In short, symptoms of Colorectal cancer include:
- Blood in stools
- Dark coloured stools, typically mixed with blood
- Change in bowel movements (due to obstructed stool movement)
- Narrowing of stools (when the left colon becomes narrow)
Diagnosis of Colon cancer / colorectal cancer
Colonoscopy is the most common method in which a thin tube like device with light and camera called Colonoscope is inserted through the anus and run through the large intestine to look for tumors or polyps. If polyps are found, a sample of polyps is taken and sent to the pathology lab to see if the cancer cells have developed in it.
Sigmoidoscopy is a procedure similar to colonoscopy in which the instrument called sigmoidscope that is shorter than a colonoscope is used to check for the presence of tumors or polyps in the rectum or sigmoidal colon area.
If the polyps confirm the presence of cancer cells, further tests such as CT Scan of liver, lungs, abdomen or PET (Positron Emission Tomography) scans are done to check for the spread of cancer in the body. Some urologists may request ‘Tumour Marker’ blood test called ‘Carcinoembryonic Antigen (CEA)’ test which looks for CEA in the blood. Higher levels of CEA typically indicate the presence of cancer cells. There are cases (such as smokers) where higher levels of CEA are found in a person but he/she is absolutely free of cancer. Depending on the stage of colon cancer, treatment methods will be suggested by your urologist or urogynecologist.
In our following article, we will be talking about staging colorectal cancer and treatment options with some frequently asked questions about Colon/colorectal cancer.