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 Colorectal cancer is, as the name suggests, cancer that occurs in the colon or rectum.

You have probably heard it referred to as colon cancer. The reason that colon and rectal cancers are grouped together in this way is because they have many features in common.

Colorectal cancer starts off, like most cancers, as a growth. This growth is found on the inner lining of the colon or rectum and is referred to as a polyp.

A polyp is not automatically referred to as cancer and some polyps never turn cancerous. However, all colorectal cancers do arise from polyps so it’s important to keep them in check.

In this article, we are going to have a look at how colon cancer starts and spreads, and then how colorectal cancer screening can help increase your treatment options.

Before we jump into that, let’s have a look at the basic structure and function of the colon and rectum.

This will help in one’s understanding of colorectal cancer.



The Structure and Function of the Colon and Rectum

The colon and rectum are part of the gastrointestinal system which, as you know, is responsible for digestion.

The colon, a muscular type, comprises most of the large intestine coming in at around 1.5m long.

It is split into four sections anatomically with each section named according to the way in which food travels through it.

These four sections are the ascending colon (travels upward from the right side of the abdomen), the transverse colon (goes across the body from right to left), the descending colon (travels down from the left side), and the sigmoid colon (due to it’s “S” shape) which joins the rectum.

There is still water and salt in the food matter after it has passed through the small intestine. This is where the function of the colon comes in – it absorbs any water and salt that is still in the remaining food matter.

What’s left after this process then goes into the rectum where it is stored until leaving the body.

In short, your colon is crucial for extracting water and other key nutrients from waste material.


How Colon Cancer Starts and Spreads

As mentioned earlier, most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are referred to as polyps. 

They come in a variety of shapes and sizes with different polyps carrying varying risks for going on to develop into cancer. 

Apart from cancer-susceptibility between the polyps, there are also general factors that can increase someone’s risk of developing colorectal cancer. 

They can be summarised as follows: 

  • Size: If a polyp larger than 1 cm is found
  • Number: If more than 3 polyps are found
  • Dysplasia: This is a pre-cancerous condition where the tissue area contains cells that look abnormal but are not yet cancerous. If dysplasia is seen in the polyp after it is removed, then it could imply an increased risk of developing colorectal cancer. 

Now let’s take a look at the variation between the actual polyp types:


  1. Adenomatous polyps: These are a common type of polyp which appear as gland-like growths. On the surface, the polyp tissue looks very much like the normal lining of your colon although it is different in a number of ways when looked at under a microscope.

    There are two major growth patterns: tubular and villous. Although many adenomas have a combination of these growth patterns and are referred to as tubulovillous adenomas.

These patterns help one’s doctor determine when the next colonoscopy needs to be done to ensure that colon cancer does not develop in the future.

 2.  Hyperplastic polyps and inflammatory polyps: This refers to a further categorization of polyps. This category is referred to as non-neoplastic polyps which do not typically become cancerous.

 Inflammatory polyps may be seen with ulcerative colitis or Crohn’s Disease.

 3.  Sessile serrated polyps and traditional serrated adenomas: These polyps fall under the neoplastic category which can be pre-cancerous and it’s normally recommended to remove them.

 “Sessile” polyps refer to those that grow as slightly flattened, broad-based polyps whereas “serrated” polyps have a saw-tooth appearance under a microscope.

 Anyone can develop colon polyps but there are heightened risks if you are over the age of 50 or if you are overweight or a smoker.

 A personal or family history of colon polyps or colon cancer is also a significant risk factor for future polyp growth.

 This leads us to the next part of our article: screening.

 Colon polyps often don’t cause any symptoms so it’s crucial to go for regular screening tests so that colon polyps can be found in as early a stage as possible.

 This will allow for a higher chance of safer and more complete removal thereby dramatically reducing the chances of developing colorectal cancer.




Why Colorectal Cancer Screening is Important


Colorectal screening is a test where doctors look for precancerous polyps so that they can be removed before turning into cancer.

 Colorectal cancer can also be found with screening tests. These tests are done to look for a disease when a person does not exhibit symptoms.

 Regular and early screening is key to preventing cancer. More screening has resulted in a significant drop in the number of colorectal cancer cases.

 In the U.S., for example, where colorectal cancer is a leading cause of cancer death for men and women, has seen a steadily declining death rate for the past several decades.

 Colorectal screening is responsible for this improved survival rate – when colorectal cancer is found early, the 5-year relative survival rate is 90%. A significant figure.

 The only factor preventing the death rate from declining even further is the fact that a large percentage of those susceptible to colorectal cancer never get screened.

 There are various reasons for this but one of the most significant is that of people simply not knowing that regular screening could save their lives from this disease. 

Education is key and is the premise behind providing you, our dear reader, with articles such as this one.

Do the right thing for you and your loved ones, get a screening done.


Types of Colorectal Cancer Screening Tests

Now that we know why it’s important to get tested, let’s take a look at the different tests that you may encounter when you go for your screening.

 There are two main groups of testing: 

1.    Structural Exams

The physical structure of the colon and rectum is studied in order to find any abnormal areas, should there be any.

In general, these tests are performed using either a scope put into the rectum or with special imaging tests.

 A colonoscopy, for example, is a type of structural (or visual) exam. The doctor uses a colonoscope (a thin flexible tube equipped with a light and small video camera) to observe the physical structure of the colon and rectum. 

The doctor can also add additional instruments to the colonoscope for the purposes of taking a sample or remove certain polyps. 

For those that would like a less invasive test, a CT colonography is also an option.

 It serves as a “virtual colonoscopy” where x-rays and a CT scan are used to build a 3D representation of the colon and rectum structure. 

These tests do require more preparation ahead of time and can’t be done as frequently as the second type of testing group.

2.    Stool-based tests

This type of testing is less invasive than visual exams and requires less preparation by the patient but it does need to be done more frequently.

 It involves a check of the stool for signs of cancer.

 Two examples of stool-based tests include the faecal immunochemical test (FIT) and the guaiac-based faecal occult blood test (gFOBT). 



Colon polyps are common but they don’t always exhibit any symptoms. This can falsely lead people to believe that they don’t have polyps and therefore don’t need to worry about colorectal cancer.


The only way to be certain is to go for regular screening tests to ensure that any signs of cancer or pre-cancerous polyps are caught and treated as early as possible.


For more information on all things gastrointestinal, visit us at www.gidoc.co.za where we can help you navigate the tricky landscape of the gut. 


The information on this website is to provide general guidance. In no way does any of the information provided reflect definitive medical advice and self-diagnoses should not be made based on information obtained online. It is important to consult a Gastroenterologist or medical doctor regarding ANY and ALL symptoms or signs including, but not limited to: abdominal pain, haemorrhoids or anal / rectal bleeding as it may a sign of a serious illness or condition. A thorough consultation and examination should ALWAYS be performed for an accurate diagnosis and treatment plan. Be sure to call a physician or call our office today and schedule a consultation.

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© Dr. Eduan Deetlefs, Registered Gastroenterologist, GI Doc Cape Town

Our website information is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. Please consult a doctor about your specific condition. Only a trained physician can determine an accurate diagnosis and proper treatment.