Colorectal Cancer

Statistically, one in ten diagnosed cancers are colorectal cancer. This puts colorectal cancer in third place on the list of the most common types of cancer worldwide. Although it is more common in men, colorectal cancer affects women too. In most cases it is found in people who are older than fifty, but this is not a rule, younger patients can also get it. 

Similar to other diseases, colorectal cancer has certain risk factors which affect the probability of its development. We will discuss all of these risk factors in this article but first, let’s try to explain what colorectal cancer really is.

What is colorectal cancer?

The development of cancer in the rectum or the colon is referred to as colorectal cancer. When mutations occur in the epithelial cells of the wall of the colon or the rectum, the abnormal growth of those cells is triggered. The mutations can be triggered by other conditions or be a result of certain lifestyle habits. These are what we refer to as “risk factors.” In some cases, the mutations can also be inherited.

The APC gene, which is involved in the process of cell adhesion and beta-catenin regulation, is usually the mutated gene responsible for the development of colorectal cancer. The malfunctioning of the APC gene allows the beta-catenin to accumulate and bind to the cellular DNA.  As a consequence, the oncogenes (genes with the potential to cause cancer) are activated.

Colorectal cancer is diagnosed by sampling the tumor tissue through a colonoscopy or sigmoidoscopy and its microscopic examination. The follow-up CT or MRI screening is usually performed to determine the extent of the disease. When colorectal cancer hasn’t spread further than the wall of the rectum or the colon, it can be cured surgically. In later stages, the spreading of cancer determines the treatment (chemotherapy, radiation, targeted therapy, etc.) and the outcomes.

Colorectal cancer symptoms

In different stages of the disease, colorectal cancer may have different symptoms. Also, the position of the tumor inside the large intestine can determine the signs and symptoms. Nevertheless, there are certain common symptoms of colorectal cancer which are present in the majority of cases. These are:

  • Blood in the stool
  • Constipation (sometimes severe)
  • Thin stool (pencil-like)
  • Loss of weight
  • Loss of appetite
  • Nausea
  • Vomiting

Colorectal cancer can be cured when it is discovered at an early stage. Unfortunately, this early stage is rarely symptomatic. This means that the only reliable method of early detection remains the regular and timely screening.

Non-modifiable risk factors of colorectal cancer

If something can increase the individual’s chances of developing a disease, it is recognized as a risk factor. There is not always a way for us to do something in order to decrease the effects of those risk factors as some of them, such as old age, cannot be changed.

On the other hand, this does not mean that the presence of some or many of the risk factors will always result in the development of the disease such as cancer. Likewise, the absence of the risk factors is not a guarantee that someone is safe from developing such diseases.

The topic of colorectal cancer risk factors is a very well researched one. Scientists have agreed on quite a few of these risk factors and they can be divided into two main groups: the risk factors that cannot be influenced by our decisions and behavior (non-modifiable risk factors) and those that can (modifiable risk factors).

Non-modifiable risk factors

A family history of colorectal cancer

Statistics show that around 33% of patients newly diagnosed with colorectal cancer have a family member who was also affected by the condition. It is not completely clear if the genetic factors are to be blamed for this. Still, precaution and regular screenings are advised to people who have had a close relative (mother, father, sibling, child, etc.) suffering from colorectal cancer or adenomatous polyps. Adenomatous polyps have the potential to become cancer and they are considered a risk factor.

Old age

As it was mentioned before, most cases of colorectal cancer are diagnosed in people older than fifty. Because of the increased risk, regular screenings are advised to people belonging to this age group while those with the family history of the disease should start with the screenings earlier, before the age of forty-five.

History of colorectal polyps

People who have a personal history of colorectal polyps are at a higher risk of developing colorectal cancer. If the polyps are numerous, large in size, or showing the signs of abnormal tissue growth (dysplasia), the risk is even higher.

A personal history of colorectal cancer is an extremely significant risk factor. People who have had the previous colorectal cancer surgically removed have a better chance for the development of a new tumor in another area of the colon or the rectum.

Ethnic and racial background

The records show that some populations are more likely to develop colorectal cancer. In the United States, the African-American population has the highest incidence of colorectal cancer and the highest mortality rate.

Ashkenazi Jews are another ethnic group prone to developing this disease. People who belong to any of the two groups should consider starting regular screenings earlier in life, especially if they have other risk factors as well.

Other non-modifiable factors

Previous treatments for various types of cancer, most notably the radiation treatment, are sometimes connected with the development of other cancers, including colorectal cancer.

Changes in melatonin levels (e.g. frequent night-shift work) are recently being linked with the increased risk of colorectal cancer. This is still a subject of research.

Health conditions that may cause colorectal cancer

Conditions that cause the inflammation of the colon over long periods of time, such as the ulcerative colitis, Crohn’s disease, and Inflammatory Bowel Disease, are considered as risk factors for colorectal cancer. This is especially true if these conditions are left untreated.

History of Inflammatory Bowel Disease (IBD)

Conditions like Inflammatory Bowel Disease (IBD) can cause the cells of the colon and rectal wall to show signs of dysplasia (abnormal growth). Over time, those cells can transform into cancer. Inflammatory Bowel Disease (IBD) is not to be confused with the Irritable Bowel Syndrome (IBS) which is not associated with the increased colorectal cancer risk.

Type 2 diabetes

Type 2 diabetes is connected with the increased risk of developing colorectal cancer. It is not clear if this connection is due to the shared modifiable factors such as obesity and physical inactivity or the diabetes itself. Hyperinsulinemia (higher than normal levels of insulin in the blood) which is common in Type 2 diabetes is thought to enhance the growth of cancer cells.   Statistics also show that the colorectal cancer mortality rate is higher for people with Type 2 diabetes.

Inherited syndromes

Inherited syndromes are responsible for around one in every twenty colorectal cancer cases. These are caused by genetic disorders which run in a family and there are several types:

  • Lynch syndrome is an inherited malfunction of the DNA repairing MLH1 or the MLH2 genes. This syndrome is responsible for up to 4% of all colorectal cancers. It is not uncommon for people with the Lynch syndrome to develop colorectal cancer at a young age. When they do not, the risk remains high throughout life. Other types of cancer are also connected with the Lynch syndrome.
  • Familial adenomatous polyposis (FAP) is characterized by the development of an extremely large number of polyps in the colon and rectum of the affected person at a young age. The risk of developing colorectal and other types of cancer is very high for people with FAP.
  • Familial adenomatous polyposis also has three sub-types:
    • Turcot syndrome, characterized by the high probability for colorectal polyps, colorectal cancer, and brain cancer.
    • Gardner syndrome is a subtype of familial adenomatous polyposis associated with the development of benign tumors of the bones, skin, and soft tissues.
    • AFAP or attenuated familial adenomatous polyposis is a milder version of FAP, distinguished by a lesser number of polyps.

Other inherited syndromes, such as the MYH-associated polyposis (MAP) and the Peutz-Jeghers syndrome, which is characterized by the growth of particular polyps called hamartomas, are also associated with a risk of an early development of colorectal cancer.

A common trait of all inherited syndromes which are recognized as risk factors for colorectal cancer is that they lead to the development of the disease at an unusually young age. Additionally, all inherited syndromes are connected with a high risk for other types of cancer.

Modifiable risk factors of colorectal cancer

Modifiable risk factors can be changed as they depend on our lifestyle, habits, and diet.


It is not fully understood how consumption of certain types of foods increases the risk of colorectal cancer, but statistics show that some diets do have a connection with this disease. Western-style diet, which is rich in fat and low in fiber, is usually associated with a higher risk of colorectal cancer.

Red and processed meats, as well as fried and grilled foods, are also connected with a higher probability of developing this condition. The risk is also increased for people who move from an area in which the diet is high in fiber to a place where the diet is high in fat (e.g. Japan to the USA).

Streptococcus gallolyticus, a bacteria which normally inhabits the alimentary tract of cattle is also associated with colorectal cancer in humans. This bacteria is often consumed along with meat and dairy products.


Being overweight or obese is considered a risk factor for colorectal cancer. Those with a large waistline, especially men, are considered to have a high risk of developing the condition. Mortality rates for obese patients suffering from colorectal cancer are higher. Obesity is also connected with other risk factors such as physical inactivity and low-quality diet.

Obese people have a higher chance of suffering from some of the conditions which fall into a group of non-modifiable risk factors for colorectal cancer, such as type 2 diabetes and inflammatory bowel disease. Chronic inflammation is also associated with obesity.

Sedentary lifestyle

Physical activity is important for a number of reasons. It can complement other colorectal cancer risk factors such as obesity and diet, but it can also improve the overall health. Regular activity is associated with a lower probability of developing colorectal cancer.


This habit is connected as a risk factor with several different types of cancer, most notably the lung cancer. Statistically, non-smokers develop colorectal cancer less often, compared to smokers.

Quitting smoking is highly recommended. Cigarettes contain many cancer-causing agents, known as carcinogens. These substances can cause damage to the DNA and impair our organism’s’ ability to repair itself.

Alcohol abuse

Acetaldehyde, a product of alcohol metabolism is a carcinogen. People who drink more than one drink a day are at a higher risk of developing different types of cancer, including colorectal cancer. With more than four drinks a day that risk is increased by fifty percent. Development of colorectal polyps is also associated with heavy drinking.

The final word

Some risk factors for colorectal factors can be changed while others cannot. Regardless of the existence or non-existence of the risk factors, statistics show us that this disease is affecting an increasing number of people.  

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