Diagnosing Colorectal Cancer

For colorectal cancer and most other cancers, it’s generally true that the earlier the cancer is detected, the better the chances are of successful treatment and recovery. The problem is, you typically can never tell something is a problem until it’s, well, too late.

This is why doctors recommend colorectal cancer screening at regular intervals, especially if the risk factors present point towards an increased likelihood of developing cancer.

You might have been experiencing worrying symptoms, or perhaps it was through a routine colorectal screening test that doctors suspect cancer is afoot.

Some of the symptoms you may experience include a change in bowel habits, such as more frequent diarrhea or constipation, rectal bleeding or blood in the stool, persistent discomfort in the abdomen, such as cramps, gas or pain, and a feeling that the bowel is not totally empty after a bowel movement. You may also experience persistent weakness, tiredness, and weight loss despite no change in your diet or lifestyle. These symptoms collectively, while innocuous by themselves, often could point towards signs of colorectal cancer. If you are concerned about these symptoms lasting longer than normal, make an appointment with a healthcare professional.

Similarly, positive results from stool-based tests such as occult blood or abnormal DNA found in the stool will also warrant further investigation. Before proceeding, the doctor will ask you questions on your medical history, including your health and family history, while also looking at other risk factors.

If cancer is suspected, doctors will recommend a diagnostic colonoscopy. This exam is done by specialized doctors through a probe inserted in the intestine to look inside for any signs of polyps or cancer.

The cancer treatment depends on the tumor stage at the moment of diagnosis. Your doctor will carefully and accurately stage the tumor through several dedicated tools.

The cancer staging is based on three letters which express the tumor growth locally and distally. These letters are shown as T, N, and M.

• T stands for tumor and expresses the local growth of the tumor lesion.
• N stands for lymph nodes involvement. The lymph nodes are local stations where the tumor accumulates during its growth.
• M stands for metastasis, and it shows that the tumor has advanced in other organs outside the bowel.

The TNM stage is essential to your doctor to decide the best treatment in a personalized fashion. The doctor has different tools to determine the TNM stage.

Investigating the extent of the cancer (TNM)

After a physical examination and a digital rectal examination, the doctor will request visual examination to see the extent of the tumor growth.

Chest X-ray

This exam creates a simple 2D picture of the organs inside the body using a very small amount of radiation. The doctor uses the chest x-ray to find out if the cancer has spread to the lungs. This is a basic tool and often, the doctor might ask for a CT scan to get a more detailed image.

Computed tomography (CT) scan

The CT scan machine takes pictures of the inside of the body using X-rays at different angles. A computer combines the pictures in a detailed image for the doctor. The CT scans can be used to measure the tumor’s size and spread locally and to other organs (especially liver and lungs). Sometimes a dye, called a contrast, can be injected into the patient’s vein, or given orally (pill or liquid) to provide better details of the tumor and other organs.

Magnetic resonance imaging (MRI)

Unlike CT scans, MRI scans — as the name suggests — uses magnetic fields to create three-dimensional images of the body. This is an advanced tool for tumor staging. A contrast agent or dye is sometimes injected into a vein to ensure clarity in the images produced. MRI scan is specifically used for rectal cancer or sometimes for liver metastasis.

Ultrasound

The ultrasound uses sound waves to create pictures of the inside of the body to find out the tumor spread. A computer then converts these series of echoes into images of the organ in question. Endorectal ultrasound is commonly used to find out how deep rectal cancer has grown. However, this tool is only able to detect local tumor growth and cannot show lymph nodes or metastasis accurately. Abdominal ultrasound is used to find out, together with CT and MRI scans, if there are any metastases in the liver.

Positron emission tomography (PET) or PET-CT scan

A PET scan creates pictures of the inside of the body. A PET scan is usually combined with a CT scan. A small amount of radioactive sugar is injected in the veins. This sugar is absorbed, especially by cells that need a lot of energy. Because cancer cells use a lot of energy, they will actively absorb most of this sugar. The scanner will detect this sugar in the cancer. The sugar contains a very low amount of radiation which is too low to be harmful. PET scans are not used regularly but only when the doctor may recommend one.

Each of these tests is used to scan different parts of the body and to show the doctor how far the cancer has spread from the colon or rectum. More specifically:

• CT scans, endorectal ultrasound and MRI scans examine the colon and/or rectum for tumors. For endorectal ultrasound a probe is inserted into the rectum prior to the scan.
• Abdominal ultrasound is used to investigate the presence of tumors in other abdominal organs other than the colon and rectum, such as the liver.

Examining the cancer tissue

Cancer staging can be determined with visual examinations, but visuals alone do not provide enough information on the kind of treatment that will be suitable for that cancer stage.

A biopsy, which is a small sample of the tumor, is necessary to investigate the type of cancer. The small amount of tissue in the biopsy is examined under a microscope by a pathologist who is a doctor specialized in studying the tumor cells.

The biopsy can be collected:

• During a screening or diagnostic colonoscopy by inserting a small instrument through the colonoscope to cut the tissues from the colon wall.
• Through a CT-guided needle biopsy, where a fine needle is inserted directly into a tumor with the help of CT imaging, and a syringe is used to pull out a piece of tissue.
• From the tissue removed after surgery.

Lab tests include detecting the presence or absence of genes that are indicators that the cancer has metastasized. This will help determine the sort of treatment that is needed, as certain targeted therapy drugs may not work if certain genetic mutations are present.