Understand colorectal cancer

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

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 Cancer (CRC) Happens When Cancer Cells Form in the Tissues of the Colon or the Rectum, 2 Parts of the Body's Digestive System

Colorectal cancer happens when cancer cells form in the tissues of the colon or the rectum, 2 parts of the body’s digestive system. 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 age 50. Having a parent, brother, sister, or child with colorectal cancer doubles a person’s risk of colorectal cancer. African Americans have an increased risk of colorectal cancer and death from the disease compared to other races.

Types of cancers in the colon and rectum

Adenocarcinoma is the most common type of colorectal cancer. Adenocarcinomas develop in the cells that make the mucus that lubricates the inside of the colon or rectum. If you’re diagnosed with colorectal cancer, it is most likely 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

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 IV (4), with stage IV (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, abnormal cells are found in the mucosa (innermost layer) of the colon or rectal wall. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called carcinoma in situ.

Stage I (1) colorectal cancer

In stage I 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 II (2) colorectal cancer

Stage II colon or rectal cancer is divided into stages IIA, IIB, and IIC.

In stage IIA

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

In stage IIB

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).

In stage IIC

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

Stage III (3) colorectal cancer

Stage III is divided into stages IIIA, IIIB, and IIIC.

In Stage IIIA

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 IIIA 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.

In stage IIIB

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

In stage IIIC

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 IIIC can be

Cancer has spread through the muscle layer of the colon or rectum wall to the serosa (outermost layer) of the 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 IIIC 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 IV (4) colorectal cancer

Stage IV is divided into stages IVA, IVB, and IVC.

In stage IVA

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

In stage IVB

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

In stage IVC

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 has spread or can’t be removed by surgery and has been shown to have certain biomarkers.

What’s next

Types of scans for cancer

Common cancer treatments

Who is on your care team