Colorectal cancer: Types, Stages and Diagnosis

Most people with early colorectal cancer don't have any symptoms. For this reason screening tests are important which can find or help prevent colorectal cancer before any symptoms develop.

Updated: June 16, 2022

Cancer starts when cells in the body start to grow out of control. Colorectal cancer may be benign, or non-cancerous, or malignant. A malignant cancer can spread to other parts of the body and damage them.

Types of Colorectal cancer:

Most of colorectal cancers are adenocarcinomas. These cancers start in cells that make mucus to lubricate the inside of the colon and rectum. Other, much less common types of tumors that can start in the colon and rectum include:

Carcinoid tumors:

These tumors starts from special hormone making cells in the intestine. They are one type of Gastrointestinal Carcinoid Tumors.

Gastrointestinal stromal tumors (GISTs):

These tumor start from special cells in the wall of the colon called the interstitial cells of Cajal. Some of them are benign. These tumors can be found anywhere in the digestive tract, but are not common in the colon.


These are cancers of immune system cells. They mostly start in lymph nodes, but they can also start in the colon, rectum, or other organs.


These tumors can start in blood vessels, muscle layers, or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.

Stages of Colorectal cancer:

The process of determining how far the cancer has spread is called staging. The stage of a cancer describes how much cancer is in the body. It helps determine how serious the cancer is and helps chose the most appropriate treatment.
The stages of colorectal cancer are:
  • Stage 0: This is the earliest stage, when the cancer is still within the mucosa, or inner layer, of the colon or rectum. It is also called carcinoma in situ.
  • Stage 1: The cancer has grown through the inner layer of the colon or rectum but has not yet spread beyond the wall of the rectum or colon.
  • Stage 2: The cancer has grown through or into the wall of the colon or rectum, but it has not yet reached the nearby lymph nodes.
  • Stage 3: The cancer has invaded the nearby lymph nodes, but it has not yet affected other parts of the body.
  • Stage 4: The cancer has spread to other parts of the body, including other organs, such as the liver, the membrane lining the abdominal cavity, the lung, or the ovaries.
  • Recurrent: The cancer has returned after treatment. It may come back and affect the rectum, colon, or another part of the body.
In many cases, diagnosis occurs at an advanced stage, when surgery is likely the best option.

Diagnosis of Colorectal Cancer:

Most people with early colorectal cancer don't have any symptoms. For this reason screening tests are important which can find or help prevent colorectal cancer before any symptoms develop.
The test include:

Medical history and physical exam:

Your medical history will be asked by your doctor to know about possible risk factors, including your family history. You will also be asked if you are experiencing any symptoms and, if so, when they started and how long you have had them.
Your doctor will also check your abdomen for masses or enlarged organs, and examine the rest of your body as a part of the physical examination. A digital rectal exam (DRE) will be done in which the doctor inserts a lubricated, gloved finger into your rectum to feel for any abnormal areas. A stool test can be done to see if it contains blood that is not visible to the naked eye which is called as occult blood.

Blood tests:

Certain blood tests are done to help determine if you have colorectal cancer. These tests also can be used to help monitor your disease if you have been diagnosed with cancer. These include:

Complete blood count (CBC):

This test measures the different types of cells in your blood. A low count in red blood cell indicates that you have anemia. Because the tumor has been bleeding for a long time, some people with colorectal cancer become anemic. But not all cancers cause a loss of blood, or they may not bleed all the time. Therefore, this test can give a false negative result. Blood may also be present because of other illnesses or conditions, such as hemorrhoids.

Liver enzymes:

Because colorectal cancer can spread to the liver, a blood test to check your liver function can be done.

Tumor markers:

Colorectal cancer cells sometimes make substances called tumor markers that can be found in the blood. Carcinoembryonic antigen (CEA) and CA 19-9 are the most common tumor markers for colorectal cancer. Blood tests for these tumor markers can sometimes indicate the presence of colorectal cancer, but they can't be used alone for diagnosis of cancer. This is because tumor marker levels can sometimes be normal in someone who has cancer and can be abnormal for reasons other than cancer.
These test are used most often along with other tests to monitor patients who already have been diagnosed with colorectal cancer. They may help show how well treatment is working or provide an early warning that a cancer has returned.

Stool DNA test:

This test is used to analyze several DNA markers that colon cancers or precancerous polyps cells shed into the stool. The stool sample will be collected by the patient and then sent to a laboratory for analysis. This test is more accurate for detecting colon cancer than polyps, but it cannot detect all DNA mutations that indicate that a tumor is present.

Flexible sigmoidoscopy:

Sigmoidoscope is a flexible, slender and lighted tube, used by a doctor to examine the patient's rectum and sigmoid. The sigmoid colon is the last part of the colon, before the rectum. The test takes a few minutes to perform and is not painful, but it might be uncomfortable. There is a small risk of perforation of the colon wall during the process. If any polyps or colon cancer is detected, then a colonoscopy can be used to examine the entire colon and take out any polyps that are present. These will be examined under a microscope. A sigmoidoscopy will only detect polyps or cancer in the end of the colon and the rectum. However, it can not detect a problem in any other part of the digestive tract.

Barium enema X-ray:

A contrast dye of barium in an enema form is placed into the bowel of the patient. Air is also added in a double-contrast barium enema. The barium fills and coats the lining of the bowel, creating a clear image of the rectum, colon, and occasionally of a small part of small intestine of the patient. Any small polyps that may have missed in this process can be detected by aflexible sigmoidoscopy. A colonoscopy is recommended if any abnormality is found in barium enema X-ray.


A colonoscope is a long, flexible, slender tube, attached to a video camera and monitor. The entire length of the colon and rectum can be seen with a colonoscope. It is inserted through the anus and into the rectum and the colon. Any polyps discovered during this exam can be removed during the procedure. Sometimes tissue samples, or biopsies, are taken for any suspicious-looking areas.
Colonoscopy is painless, but a mild sedative are given to some patients in order to calm them down. The patient may be given laxative fluid to clean out the colon before the test. An enema is rarely used in this process. Bleeding and perforation of the colon wall are possible complications which is very rare.


In case any rectal cancer is suspected, a protoscopy is done. The doctor will look inside the rectum with a proctoscope, which is a thin, rigid, lighted tube with a small video camera on the end. It is inserted through the anus. The inside lining of the rectum through the scope can be seen closely by your doctor. The tumor can be seen, measured, and its exact location can be determined. For example, how close the tumor is to the sphincter muscles that control the passing of stool can be viewed.


If a suspected colorectal cancer is found by any screening or diagnostic test, it is biopsied during a colonoscopy. In a biopsy, a small piece of tissue will be removed by the doctor with a special instrument passed through the scope. Sometimes a part of the colon may need to be surgically removed to make the diagnosis which is very rare. Biopsy samples are then sent to the lab to investigate under a microscope. Other lab tests may also be done on the biopsy specimens to help better classify the cancer if cancer is found.

MSI and MMR testing:

Specific gene changes in the cancer cells will also looked by the doctor as that might affect how the cancer is treated especially if the cancer has spread. 
Colorectal cancer cells are typically tested to see if they show high levels of gene changes called microsatellite instability (MSI). Testing might also be done to see if the cancer cells have changes in any of the mismatch repair (MMR) genes such as MLH1, MSH2, MSH6, and PMS2.
Changes in MSI or in MMR genes or both are often seen in people with Lynch syndrome. Most colorectal cancers do not have high levels of MSI or changes in MMR genes. But as most colorectal cancers are linked to Lynch syndrome, these tests are done in some cases.
There are two possible reasons to test colorectal cancers for MSI or for MMR gene changes:
  • To identify patients who should be tested for Lynch syndrome. A diagnosis of Lynch syndrome can help plan other cancer screenings for the patient. For example, women with Lynch syndrome may need to be screened for uterine cancer. Also, if a patient has Lynch syndrome, their relatives could also have it, and may want to be tested for it.
  • To determine treatment options for colorectal cancer, where MSI or MMR results could change the way it is treated.

Imaging tests to look for colorectal cancer:

Imaging tests use sound waves, x-rays, magnetic fields, or radioactive substances to create images of the different parts of your body. Imaging tests may be done to look at suspicious areas that might be cancer, see how far cancer has spread and help determine if treatment is working.

Computed tomography (CT or CAT) scan

A CT scan uses x-rays to make detailed cross-sectional images of your body. This test is done to see if colon cancer has spread into your liver or other organs.


Ultrasound uses sound waves and their echoes to create images of the inside of the body. A small microphone like instrument called a transducer gives off sound waves and picks up the echoes as they bounce off organs which are then converted by a computer into an image on a screen.
Depending on the location, there are different types of ultrasound. These include:

Abdominal ultrasound:

A technician moves the transducer along the skin over your abdomen in this procedure. This test can be used to look for tumors in your liver, gallbladder, pancreas, or elsewhere in your abdomen, but it can't look for tumors of the colon.

Endorectal ultrasound:

This test uses a special transducer that is inserted into the rectum. It is used to see how far through the rectal wall a cancer has grown and whether it has reached nearby organs or tissues such as lymph nodes.

Intraoperative ultrasound:

This exam is done during surgery. The transducer is placed directly against the surface of the liver, making this test very useful for detecting the spread of colorectal cancer to the liver. This allows the surgeon to biopsy the tumor, if one is found.

Magnetic resonance imaging (MRI) scan:

MRI scans uses radio waves and strong magnets instead of x-rays to show detailed images of soft tissues in the body. A contrast material called gadolinium may be injected into a vein before the scan to see the images in more detail. MRI can be used to look at abnormal areas in the liver or the brain and spinal cord that could be cancer spread.
MRI scans can be used in patients with rectal cancers to see if the tumor has spread into nearby structures. This is called as endorectal MRI where a probe, called an endorectal coil is placed inside the rectum. This stays in place for 30 to 45 minutes during the test and can be uncomfortable.. This can help plan surgery and other treatments.

Chest x-ray:

An x-ray may be done after colorectal cancer has been diagnosed to see if cancer has spread to the lungs.

Positron emission tomography (PET) scan:

PET scans  usually use a form of radioactive sugar that is put into the blood. Depending on how fast the body cells are growing, they take in different amounts of the sugar. Cancer cells, which grow quickly, are more likely to take up larger amounts of the sugar than normal cells. A special camera is used to create a picture of areas of radioactivity in the body.
The picture from a PET scan is not as detailed as a CT or MRI scan, but it provides helpful information about whether abnormal areas seen on these other tests are likely to be cancer or not and how far it has spread. This test is usually done to see if the cancer has spread to lymph nodes or other parts of the body if you have already been diagnosed with cancer.


Angiography is an x-ray test for looking at blood vessels. A contrast dye is injected into an artery, and then x-rays are taken. The dye outlines the blood vessels on x-rays. This test can show the arteries that supply blood to the tumors if the cancer has spread to the liver. This can help surgeons decide if the liver tumors can be removed and if so, it can help plan the operation. Angiography can also help in planning other treatments for cancer spread to the liver, like embolization.

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