Colon cancer happens when tumors grow in the large intestines. The colon, most commonly known as the large intestine, is where the body extracts water and salt from solid waste, which then moves through the rectum and out of the body.

While watching for colon cancer symptoms doesn’t frequently cross our minds, knowing the signs of what is considered unusual can help prevent something from becoming too serious.

Understanding Colon Cancer

Colon cancer is the third leading cause of cancer in both men and women in the U.S. In most cases, colon cancer develops from precancerous polyps that line the inner walls of the large intestines.

There are two different types of polyps:

  • Adenomas: These polyps tend to look similar to the lining of the colon, but once they are looked at under a microscope, they take on a unique look. While they are usually benign, adenomas that aren’t removed can become cancerous.
  • Hyperplastic Polyps: These are typically benign, and cancer doesn’t usually result from them. They are considered a growth of extra cells that project from the tissue of the colon, generally in areas where your body had repaired damaged tissue.

In many cases, these polyps are found through routine colon screenings, and once found, they are removed. While removal of these polyps helps to prevent colon cancer, it doesn’t guarantee that the patient won’t end up with cancer.

Once these masses become cancerous tumors, there is a chance that cancerous cells may spread throughout the body. This process is called metastasis, and since the cancerous cells spread through the blood and lymph systems, they invade healthy tissues, resulting in a more serious, less treatable condition.

Colon Cancer Screenings

In most cases, colon cancer is found either through symptoms noticed by patients or through regular colon screenings.

So what kind of screenings can be done to help find colon cancer? According to the American Cancer Society, several testing options fall under two categories: stool-based tests and visual exams of the colon and rectum.

Stool-Based Tests

Digestive system

Multiple tests make use of stool samples to check for colon cancer. These tests allow patients to collect their own stool samples at home and either mail them in for testing or by returning them to their doctor’s office.

While many find that these tests are more comfortable than the ones done in the office, these tests need to be done more regularly.

  • Fecal Immunochemical Test (FIT) – This test looks for hidden blood in the stool. It reacts to part of the human hemoglobin protein, which is found in red blood cells. It requires a collection of a small amount of stool, and no drugs are needed to be taken for sample collection.
  • Guaiac-Based Fecal Occult Blood Test (gFOBT) – This test looks for hidden blood in the stool through a chemical reaction, in a different manner than FIT. This test can be done at home and allows you to check multiple samples.
  • Multitargeted Stool DNA Test (MT-sDNA) – This test looks for certain abnormal sections of DNA from cancer or polyp cells. These cells often have DNA mutation in specific genes, and these cells usually get into the stool. The sample can be collected at home.

Visual (Structural) Exams of the Colon and Rectum

Colon and Rectum

Visual tests take a look at the structure inside of the colon and the rectum. Doctors look for any abnormal areas that could be cancerous tumors or polyps. While these exams can be done less frequently, they do require more preparation ahead of the exam and can have some risks.


This test requires the patient to have a completely clean colon and rectum, so the system is often cleansed with the use of liquid laxatives and enemas. The doctor will then look at the entire length of the colon and rectum with a colonoscope.

A colonoscope is a flexible tube about the width of a finger that has a small light and video camera on the end of it. It is inserted through the anus and then up the rectum and colon. Small instruments can then be passed through the colonoscope to biopsy or remove anything that looks suspicious, such as polyps.

CT Colonography (Virtual Colonoscopy)  

Much like a colonoscopy, before the test, a patient must clean their system with the use of liquid laxatives. This test uses a CT to take x-rays of the colon. This test creates both 2-dimensional x-ray pictures and a 3-dimensional view of the inside of the colon and rectum. This allows doctors to check for tumors or polyps.

Flexible Sigmoidoscopy (FSIG)

After significant prep to clean and empty your insides, this test makes use of a sigmoidoscope to allow the doctor to see the inner lining of the colon and rectum better.

This procedure involves pumping air into the colon and rectum, so the doctor can get a better look at the lining of both and to check for tumors or polyps. If polyps are found, they can then remove them with a small instrument that is passed through the scope.

10 Common Colon Cancer Symptoms to Watch For

While the best way to identify colon cancer is through regular examinations, there are some symptoms that patients can watch for.

Colon cancer symptoms can be hard to identify because they are pretty general and could be caused by any number of conditions. What is important is to know what is out of the ordinary for your body and, once you spot something is off, to get a hold of your doctor as soon as possible.

Below, we have listed 10 of the most common colon cancer symptoms that patients should keep an eye out for:

1. Anemia


Anemia, which is also known as an iron deficiency, is a condition resulting from abnormally low levels of red blood cells. This often occurs when the body doesn’t make enough blood, loses blood, or the body destroys red blood cells.

2. Fatigue


While fatigue isn’t typically something to worry about, excessive fatigue with persistent physical, emotion and mental exhaustion is something worth noting. This sort of fatigue not only interferes with daily life, but it does not improve with rest and can affect mood, emotions, and even job performance.

3. Unexplained Weight Loss


Any unusual changes in weight should be carefully monitored and reported to your doctor, but when it comes to unexplained and unintentional weight loss, patients need to be careful. This sort of weight loss can be a result of any number of conditions, all of which should be checked out.

4. Change in Bowel Habits

man using the restroom

Changes in bowel habits can mean going from regular to having diarrhea, constipation, and even just having the feeling of having to go but not being able to.

5. Shortness of Breath

man having shortness of Breath

Shortness of breath can be a result of a slow, internal bleeding. According to Dr. Patricia Raymond, an American College of Gastroenterology fellow quoted in a Reader’s Digest article, if you aren’t bleeding aggressively or vomiting blood, “your body puts more plasma in the blood without making more iron or red blood cells.”

This prevents the body from losing blood in a significant amount, though it reduces the blood’s ability to carry oxygen, which is why some experience shortness of breath.

6. Feeling Bloated/Crampy

 Feeling Bloated/Crampy

Excessive bloating, cramps and general feelings of fullness can be a red flag if it’s happening out of the blue or more frequently than usual. While these symptoms can be any number of things, if it is persistent, then it needs to be addressed.

7. Severe Constipation

holding a tissue

Occasional constipation isn’t something to worry about, but once it becomes frequent or doesn’t seem to ease up, then it’s time to talk to the doctor. Constipation is a sign that there is some sort of blockage, and obstructions of any type, for any amount of time, are unhealthy, so make sure to get your constipation checked out ASAP.

8. Color Change in Stool

woman urinating

Depending on a patient’s usual diet, a slight change in the color of their stool can merely mean that they ate something a little different. Once stools begin to look dark or tarry, that is a sign that there is some blood in them. If the color change seems to be persistent or shocking, then it’s time to get to the doctor and have an exam done.

9. Unusually Skinny Stools

using toilet

Stools come in all shapes and sizes, and that can depend on what a person ate and in what quantities. However, that doesn’t mean you shouldn’t pay close attention to the size and shape of your stool. If you notice that it’s skinnier than usual and that the new size is happening more frequently, that could be a sign of restriction in the colon. This can be due to polyps or tumors in the colon or rectum.

10. Dark/Bloody Stools 

man sitting on a toilet bowl

As mentioned before, any color change in a patient’s stool should be noted and investigated, but if their stool is consistently dark or mixed with dark red spotting or even fresh blood in the toilet, it is time to get a professional opinion. Blood of any kind in the toilet is a red flag that something is wrong, so do not hesitate and get to the doctor as soon as you can.

Colon Cancer Can Be Silent

Colon cancer symptoms aren’t always the most obvious ones to notice, and when they do become noticeable, cancer isn’t the first thing that pops into the mind. In order to prevent a severe diagnosis, it is essential to report any changes to your doctor immediately and to make sure you have your regular screenings.

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