Understand colorectal cancer

Colorectal cancer (CRC) is the third most common cancer in the United States, excluding skin cancer.

The information on this page may help you gain a better understanding of your colorectal cancer diagnosis and what’s happening to your body. This may help when making important decisions with your doctor.

What is colorectal cancer?

Colorectal (“KOH-loh-REK-tul”) means relating to or affecting the colon and rectum. Both the colon and rectum are part of the body’s digestive system. The digestive system takes food into the body and turns that food into nutrients. The material that can’t be used becomes waste. The digestive system moves this waste out of the body, with the help of the colon to the rectum, and finally to the anal canal for elimination.

Colorectal cancer happens when cancer cells form in the tissues of the colon or the rectum. These cancers can also be called colon cancers or rectal cancers, depending upon where they start. Colorectal cancer includes both colon and rectal cancer because they share many features.

Colorectal cancer usually starts as a growth on the inside of the colon or the rectum. These growths are known as polyps. Over time, some of these polyps can turn into cancer.

The risk of colorectal cancer increases after age 50. Most cases of colorectal cancer are diagnosed after this age. Having a parent, brother, sister, or child with colorectal cancer doubles a person’s risk of colorectal cancer. Black individuals have an increased risk of colorectal cancer and death from the disease compared to other races.

Types of cancers in the colon and rectum

The most common type of colorectal cancer is called adenocarcinoma (“A-deh-noh-KAR-sih-NOH-muh”). Adenocarcinomas develop in the cells that line the colon and rectum. These cells make the mucus that lubricate the inside of the colon or rectum. If you’re diagnosed with colorectal cancer, it is most likely categorized as adenocarcinoma.

There are less common types of tumors that can start/occur in the colon or rectum:

Gastrointestinal stromal tumors (GISTs) – cancer that starts in special cells inside the wall of the colon
Carcinoid tumors – cancer that starts in hormone-making cells inside the intestine
Lymphomas – cancer that primarily starts in the lymph nodes, but can also start in the colon, rectum or other organs
Sarcomas – cancer that starts in the blood vessels, muscle layers or other connective tissues, in the wall of the colon or rectum

Risk factors for colorectal cancer

Anything that increases the chance of getting a disease is called a risk factor. Some risk factors for colorectal cancer, such as smoking cigarettes, can be changed. Other risk factors, like getting older, are not within anyone’s control.

Colorectal risk factors can include:

Age: Colorectal cancer risk increases after age 50

Family history of colorectal cancer: Having a sibling, parent, or child with colorectal cancer doubles your chances of having that cancer

Race: Being Black increases the risk of colorectal cancer

Personal history of adenomatous polyps or colorectal cancer: Adenomatous polyps are growths in the colon or rectum that may turn into cancer. Having colorectal cancer in the past increases the risk for having it again

Inherited genetic syndromes: The most common of these are Lynch syndrome and family adenomatous polyposis (FAP), which are caused by mutations in a person’s genes

A history of chronic ulcerative colitis or Crohn disease for 8 years or more

Obesity

Smoking: Smoking tobacco for a long time increases the risk of colorectal cancer, as well as other cancers

Alcohol use: Drinking 3 or more alcoholic beverages a day may increase colorectal cancer risk

Talk to your doctor if you think you may be at an increased risk for colorectal cancer.

Screening

Being screened for colorectal cancer is a procedure separate from your regular doctor’s appointment. At age 45, everyone at average risk should be screened for colorectal cancer. Your doctor can refer you for this screening. Testing options include:

A stool-based test: you collect the stool sample and send it off to be tested

A visual exam: a colonoscopy (pronounced “KOH-luh-NOS-koh-pee”) is a visual examination of the colon and rectum in which an instrument is inserted into the rectum

Talk to your health care provider about which test is right for you.

In recent years, the rate of colorectal cancer in people younger than 50 years has increased 2.2% each year, with higher rates in Black and Hispanic individuals compared to White individuals. In response, the screening age for colorectal cancer was lowered to age 45 by the United States Preventive Services Task Force in 2021. Talk to your doctor about whether you or a family member should screen for colorectal cancer before age 45.

What happens after your colonoscopy?

Your doctor may find polyps during the colonoscopy and may send that tissue out to be analyzed by a pathologist. The pathologist is looking for signs of cancer. If there are no signs of cancer, your doctor will tell you when you need to be screened again.

If there are signs of cancer, your doctor will order other tests.

Diagnosis

What happens if your colorectal screening indicates cancer?

If the results of your screening show signs of cancer, your doctor will order more tests. The following are common diagnostic tests for colorectal cancer.

Medical history/physical exam

Your health care provider may take your medical and family history.

Blood tests

Your health care provider may take a blood sample through a needle placed in your vein. The tests can show signs of disease and how well your internal organs are working.

Complete blood count (CBC): This test measures the number of red and white blood cells, as well as platelets, in your blood.

Chemistry profile: This test measures the level of metabolites, electrolytes, and proteins, as well as other substances in the blood. These substances show how well your kidneys, liver and other organs are working. This test is also called a comprehensive metabolic panel (CMP).

CEA blood test: CEA stands for carcinoembryonic antigen, which is a protein found in blood. CEA is thought to be a tumor biomarker.

Imaging

Your doctor may want to see pictures of your colon and/or rectum. Common imaging tests include:

CT scan: A computed tomography (CT or CAT) scan uses x-rays to take pictures of the inside of the body. A substance called contrast will be injected into your vein for the CT scan. This substance makes the picture clearer. CT with contrast is the main imaging test used in determining the extent of colon cancer in the body.

PET scan: A positron emission tomography (PET) scan uses a radioactive drug called a tracer, which is injected into a vein and shows where cancer cells are in the body. PET scans are not used that often with colorectal cancer.

MRI scan: Magnetic resonance imaging (MRI) uses magnetic field and radio waves to form pictures.

EUS: For rectal cancer, an endorectal ultrasound (EUS) may be used instead of an MRI. For an EUS, a small probe inserted in the rectum emits sound waves that cause echoes. The echoes form a picture of the inside of the rectum.

Biomarkers commonly tested for in colorectal cancer

If you’ve been diagnosed with colorectal cancer, your doctor may order biomarker testing. A biomarker is a biological molecule which can be measured and is found in blood and other body fluids or tissues.

The presence and type of biomarkers found in your sample may help your doctor determine the treatment plan that is right for you.

All patients with colorectal cancer should undergo MMR or MSI biomarker testing

In healthy cells, a process called mismatch repair (MMR) fixes mutations when they occur in the cell. But when this process isn’t working right, the MMR system does not fix errors, causing those errors to build up. These repeated mistakes make the cell’s DNA unstable. This is called microsatellite instability (MSI).

High microsatellite instability, or MSI-H, is a biomarker for colorectal cancer. Another term for this is that the cells are “deficient” in mismatch repair, or dMMR.

There are 2 kinds of lab tests for this biomarker. Results that show your cancer has this biomarker are:

MSI-H (microsatellite instability-high)
dMMR (mismatch repair deficient)

If you are diagnosed with metastatic colon cancer, your doctor may also order tests for the following biomarkers:

KRAS and NRAS mutations: Some colorectal cancers have mutations in the KRAS and NRAS genes, which can make them overactive and cause the cancer to grow
BRAF mutation: The mutation called BRAF V600E causes cancer cells to grow and spread rapidly
HER2 amplification: HER2 is a protein that regulates cell growth. Too much HER2 can cause cancer cells to grow and spread quickly. It is recommended that everyone with metastatic colorectal cancer undergo HER2 testing, unless there is a known RAS or BRAF mutation

Ask your doctor about biomarker testing, molecular testing, genomic testing, tumor gene testing, next-generation sequencing or mutation testing. All of these phrases refer to biomarkers.

Stages of colorectal cancer

From the National Cancer Institute (NCI)

The information below is based on information originally published by the National Cancer Institute (NCI), the US government’s main agency for cancer research. Use this information to talk to your doctor about your specific stage of colorectal cancer.

Colorectal cancer is described in 5 stages ranging from 0 to 4, with stage 4 being the most severe. Some stages can also be broken down further into substages (A, B, or C).

Stage 0 colorectal cancer

In stage 0 colon or rectal cancer, abnormal cells are found in the mucosa (innermost layer) of the colon or rectum wall. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called carcinoma in situ (in situ is Latin for “in position”).

Stage 1 colorectal cancer

In stage 1 colon or rectal cancer, cancer has formed in the mucosa (innermost layer) of the colon or rectum wall and has spread to the submucosa (layer of tissue next to the mucosa) or to the muscle layer of the colon or rectum wall.

Stage 2 colorectal cancer

Stage 2 colon or rectal cancer is divided into stages 2A, 2B, and 2C.

Stage 2A:

Cancer has spread through the muscle layer of the colon or rectum wall to the serosa (outermost layer) of the colon or rectum wall.

Stage 2B:

Cancer has spread through the serosa (outermost layer) of the colon or rectum wall to the tissue that lines the organs in the abdomen (visceral peritoneum).

Stage 2C:

Cancer has spread through the serosa (outermost layer) of the colon or rectum wall to nearby organs.

Stage 3 colorectal cancer

Stage 3 colon or rectal cancer is divided into stages 3A, 3B, and 3C.

Stage 3A:

Cancer has spread through the mucosa (innermost layer) of the colon or rectum wall to the submucosa (layer of tissue next to the mucosa) or to the muscle layer of the colon or rectum wall. Cancer has spread to 1 to 3 nearby lymph nodes, or cancer cells have formed in tissue near the lymph nodes.

Or stage 3A can be

Cancer has spread through the mucosa (innermost layer) of the colon or rectum wall to the submucosa (layer of tissue next to the mucosa). Cancer has spread to 4 to 6 nearby lymph nodes.

Stage 3B:

Cancer has spread through the muscle layer of the colon or rectum wall to the serosa (outermost layer) of the colon or rectum wall or has spread through the serosa to the tissue that lines the organs in the abdomen (visceral peritoneum). Cancer has spread to 1 to 3 nearby lymph nodes, or cancer cells have formed in tissue near the lymph nodes.

Or stage 3B can be

Cancer has spread to the muscle layer or to the serosa (outermost layer) of the colon or rectum wall. Cancer has spread to 4 to 6 nearby lymph nodes.

Or stage 3B can be

Cancer has spread through the mucosa (innermost layer) of the colon or rectum wall to the submucosa (layer of tissue next to the mucosa) or to the muscle layer of the colon or rectum wall. Cancer has spread to 7 or more nearby lymph nodes.

Stage 3C:

Cancer has spread through the serosa (outermost layer) of the colon or rectum wall to the tissue that lines the organs in the abdomen (visceral peritoneum). Cancer has spread to 4 to 6 nearby lymph nodes.

Or stage 3C can be

Cancer has spread through the muscle layer of the colon or rectum wall to the serosa (outermost layer) of the colon or rectum wall or has spread through the serosa to the tissue that lines the organs in the abdomen (visceral peritoneum). Cancer has spread to 7 or more nearby lymph nodes.

Or stage 3C can be

Cancer has spread through the serosa (outermost layer) of the colon or rectum wall to nearby organs. Cancer has spread to 1 or more nearby lymph nodes, or cancer cells have formed in tissue near the lymph nodes.

Stage 4 colorectal cancer

Stage 4 colon or rectal cancer is divided into stages 4A, 4B, and 4C.

Stage 4A:

Cancer has spread to 1 area or organ that is not near the colon or rectum, such as the liver, lung, ovary, prostate or a distant lymph node.

Stage 4B:

Cancer has spread to more than 1 area or organ that is not near the colon or rectum, such as the liver, lung, ovary, prostate or a distant lymph node.

Stage 4C:

Cancer has spread to the tissue that lines the wall of the abdomen and may have spread to other areas or organs.

Learn about a possible treatment option for certain patients with advanced colorectal cancer that expresses certain biomarkers.

Recommended Books That May Help Children Understand Parent's Cancer Diagnosis

Common types of treatment

Once your doctor has confirmed your cancer diagnosis and performed the necessary tests, they will work with you to determine which treatment plan is right for you. Your doctor may recommend one or more of the following treatments:

Active surveillance (watch and wait): Undergoing tests and monitoring to see if the cancer is growing and giving no treatment unless there are changes in test results
Chemotherapy: The use of drugs to stop cancer cell growth
Cryosurgery: The use of an instrument to freeze and destroy abnormal tissue
Immunotherapy: Treatment using the patient’s immune system to fight cancer
Radiation therapy: The use of x-rays or other types of radiation externally or internally to kill cancer cells or keep them from growing
Radiofrequency ablation: Using a probe with tiny electrodes to kill cancer cells
Surgery: Removing the affected tissue
Targeted therapy: The use of drugs or other substances to identify and attack specific cancer cells

Visit Common cancer treatments for more information.

Example questions to ask your doctor

What kind of colorectal cancer do I have?
What is the stage of my cancer, and what does that mean in my case?
Based on what you’ve learned about my cancer, what is my prognosis (outlook)?
What treatment choices do I have?
Will I need more tests before we decide on treatment?
What is the goal of treatment (to remove or treat the cancer, slow its growth, ease symptoms, etc)?
Should I get a second opinion?
If surgery is recommended, is there anything else I need to do or take before or after surgery?
How quickly do we need to decide on treatment?

        
What kind of colorectal cancer do I have?
What is the stage of my cancer, and what does that mean in my case?
Based on what you’ve learned about my cancer, what is my prognosis (outlook)?
What treatment choices do I have?
Will I need more tests before we decide on treatment?
What is the goal of treatment (to remove or treat the cancer, slow its growth, ease symptoms, etc)? 
Should I get a second opinion?
If surgery is recommended, is there anything else I need to do or take before or after surgery?
How quickly do we need to decide on treatment?

What’s next

Common cancer treatments

Be involved in treatment decisions

Who is on your care team

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