What Happens When Doctors Diagnose Colon Cancer?

When faced with the possibility of colon cancer, it’s understandable to feel intimidated by the prospect of a diagnosis. However, the diagnosis and staging process is a key part of understanding what your treatment options are. The sooner that happens, the better equipped you will be.

Your doctor will take steps to diagnose the colon cancer and stage it - in other words, classify how advanced the cancer is and how far it has spread.

If you have symptoms of colorectal cancer or your regular screening reveals something abnormal, your doctor will first want to:

  1. Do a physical examination and take a medical history

  2. Perform some tests

If you detect symptoms such as abdominal pain or blood in your stool, or if you use an at-home test that gives a positive reading, see your doctor right away.

Most colorectal cancer is relatively slow-growing. If detected in its earlier stages, it can often be treated with complete success. That’s why it’s incredibly important to get a diagnosis as soon as possible.

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Your medical history and physical exam

The first step will be answering questions about your medical history to see if you have possible risk factors for colorectal cancer. One such risk, for example, is a history of it in your family.

The doctor will also want to hear about your symptoms. It is important to be as accurate as possible about what they are and how long you have been aware of them.

In your physical exam, your doctor will feel your abdomen for solid masses or enlarged organs. If cancer has advanced, it may have spread to your liver or lungs. The doctor may examine your rectum by inserting a gloved, lubricated finger to try to detect any abnormalities.

Tests and procedures

Test for blood in your stool

Blood in your stool that you notice in the toilet can be a symptom of colon cancer. However, in the earlier stages of colon cancer, when there is less blood, it may be detected only by a test.

Blood not visible to the naked eye is called occult blood. You can perform a fecal occult blood test (FOBT) or an immunochemical test (FIT) on your own stool at home. Your doctor will prescribe the testing kit and instructions. These tests are for the initial detection of possible colon cancer. They are not used to follow up a screening test that has revealed abnormalities.

Blood tests

A blood test can help your doctor diagnose colon cancer and track the disease. There are several different tests:

  • Complete blood count. This test measures the numbers of the different types of cells in your blood. This test can show, for example, if you have too few red cells (anemia). This could result from loss of blood over an extended period from a bleeding colorectal tumor.

  • Liver enzymes. Colorectal cancer may spread to the liver. A blood test can check your liver’s functioning.

  • Tumor markers. Markers are substances that may be created by disease and can be detected in the blood. Tumor markers produced by colorectal cancer cells include carcinoembryonic antigen (CEA). However, this useful test will not be definitive because high levels of CEA or another tumor marker may have other causes.


As part of your regular, preventive screening for colorectal cancer, you may have had several colonoscopies. However, if your doctor is examining you because you have symptoms or an abnormal result from another screening test, they may recommend a colonoscopy as part of the diagnosis.

This will mean using a colonoscope (a lighted tube with a small video camera at the end) to examine the whole length of your colon and rectum. The thin, flexible tube is inserted through the anus, into the rectum, then into the colon. If your doctor detects polyps or other abnormal areas, he can insert instruments through the colonoscope to perform a biopsy or remove a polyp, for example.

Your colonoscopy can be done in your doctor's office, a clinic, or a hospital’s outpatient department. This procedure can take from a half-hour to an hour and is done after you’ve received medication to relax and make you drowsy. Patients sometimes experience mild cramping because the colonoscope blows air into your colon to expand it so the doctor can see more clearly.


The rectum is a chamber connecting the anus to the end of the colon. A test specifically for rectal cancer may use a proctoscope to examine the rectum. A proctoscope is a thin, rigid, lighted tube with a video camera at the end. It is inserted through your anus so your doctor can inspect the inside lining of your rectum. If there is a tumor, it can be seen, measured, and its location precisely noted. One important issue for surgery is how close the tumor is to your sphincter, the valve that controls the passing of stool.   


It is standard to confirm suspected colorectal cancer found during screening by doing a biopsy. Your doctor can do this during your colonoscopy using a special instrument passed through the colonoscope to remove a small piece of tissue. In some cases, however, a diagnosis can be made only by removing a part of your colon.

Different types of biopsies can be performed and the samples used in the lab to diagnose colon cancer. If the lab finds cancer, other tests can be done on the samples to classify cancer and seek specific options for treatment. Treatment will depend upon the stage cancer has reached.

  • Gene tests, for example, will be important if cancer has spread. Doctors will look for specific gene changes in the cancer cells to guide their choice of the best drugs for treatment.

  • MSI and MMR tests can see if colorectal cancer cells have gene changes often seen in people with Lynch syndrome but not in most other colorectal cancers. Hereditary Nonpolyposis Colon Cancer (HNPCC), also known as Lynch syndrome, is an inherited disorder. It increases your chances of getting colon cancer because it can develop even when you have few, if any, polyps (thus "nonpolyposis"). If the lab detects changes in the MSI or MMR genes, you will be tested for Lynch syndrome, and the doctor will suggest you share the diagnosis with relatives because Lynch syndrome is hereditary.

Imaging tests

As imaging technology becomes increasingly sophisticated, doctors find more ways to diagnose colon cancer. They might use imaging tests to:

  • Noninvasively examine suspicious areas for signs of cancer

  • See if cancer has spread and how far

  • Help determine if a particular treatment is effective

  • Monitor the patient for signs of cancer coming back after treatment.

Some scanning technologies have limited application when trying to diagnose colon cancer. For example, a chest x-ray can show if cancer has metastasized to the lungs. Other scanning techniques have many more applications to cancer.

CT or CAT scanning is a more advanced type of x-ray that can indicate if your colorectal cancer has spread to your lymph nodes, liver, lungs, or other organs. CT scanning can guide a biopsy by directing a needle into the mass from which the tissue sample will be taken. Ultrasound is another means of imaging the inside of the body, in this case by bouncing sound waves off an organ and using a computer to convert the echoes into an image on a screen. By moving the sound wave source (transducer) over your abdomen, a technician can look for tumors in your liver, pancreas, or elsewhere. A different method is endorectal ultrasound, with a transducer in your rectum to see how far cancer has grown through the rectal wall and if it has invaded other organs or lymph nodes.

MRI uses magnetic resonance to show images of soft tissues in your body, such as abnormal areas in the liver or brain that might be the spread of cancer. These detailed images can also be improved by using contrast material injected into a vein before the scan. A particular application of MRI is scanning your pelvis to see if your cancer has spread. This can set the stage for surgery and other treatments. In some cases, you may get more accurate results with endorectal MRI-- a probe or endorectal coil inserted in the rectum.

PET scans involve injecting a slightly radioactive substance into the bloodstream. This finds its way mainly into cancer cells so the scan can produce an image of them.

Angiography uses x-rays to enable the doctor to examine your blood vessels. It works by injecting a contrast dye into an artery, then taking x-rays as the dye outlines blood vessels. Your doctor may want to use this if your cancer has spread to the liver because angiography can show the arteries that supply blood to tumors.

Staging colorectal cancer

The priority of all these tests is to find out if you have colon cancer. At the same time, however, many of these procedures can provide information about the type of colorectal cancer, measure how far it has advanced, and find where it is now located.

The process of determining how far cancer has advanced, the present situation, and the prospects for treatment is called staging. Staging is used with all cancers to achieve the best possible understanding of a patient’s prospects and the most promising approaches to treatment.

Colorectal cancer staging will be concerned, for example, with estimating how far cancer has penetrated from the colon and rectum into the rest of the body.

The three broad determinations are local invasion, some degree of lymph node involvement (beginning to spread), and distant metastasis into the lungs, brain, spinal cord, and other areas.

The most common basic staging system is called TNM:

  • T stands for “tumor.” In colorectal cancer, this shows how much cancer has invaded the colon wall (still local or contained in the colon). 

  • N, for "node,” is concerned with the degree of lymph node involvement. The lymph system is one of the first places local cancer spreads. 

  • M, for "metastasis,” is the spread of cancer to other parts of the body, such as the liver or the brain.

For N (node), for example, the degree of lymph node involvement might fall into these criteria:

  • No evidence of spread to regional lymph nodes

  • Tumor cells found in one regional lymph node

  • Tumor cells found in two or three regional lymph nodes

  • There are cancerous nodules near the colon that do not appear to be lymph nodes

  • Other criteria

You will undergo so many tests to diagnose colon cancer because to stage it, your doctor will need to make many refined judgments like this.

If you get screened regularly and see your doctor right away if you notice symptoms, you can be confident that your doctor, even while diagnosing you, is preparing an accurate report and the most effective treatment plan if the diagnosis is positive.

The lowdown

Colorectal cancer is among the potentially most deadly cancers. Fortunately, regular colon cancer screening will catch it in its early stages, when the chances for successful treatment and cure are optimal.

If you are being diagnosed because you have possible symptoms, your doctor has an array of tests and procedures to:

  • Make a successful diagnosis

  • Understand the progression and amount of cancer in your body (called "staging”)

  • Use the staging to make a far more accurate prognosis and decisions about the most effective treatments in your specific case.

Have you considered clinical trials for Colon cancer?

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