This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science
This page was updated on August 11, 2022.
Colorectal cancer develops in the colon or in the rectum. If it starts in the colon, it may be referred to as colon cancer. If it starts in the rectum, it may be called rectal cancer. Regardless of where they start, however, these cancers share a lot in common, which is why they’re together known as colorectal cancer.
The most common type of colorectal cancer is adenocarcinoma. Adenocarcinomas of the colon and rectum make up 95 percent of all colorectal cancer cases. In the gastrointestinal tract, rectal and colon adenocarcinomas develop in the cells of the lining inside the large intestine. These adenocarcinomas typically start as a growth of tissue called a polyp. A particular type of polyp called an adenoma may develop into cancer. Colorectal polyps are often removed during a routine colonoscopy before they may turn cancerous.
While other types of tumors may develop in the colon or rectum, they’re much more rare. Less common types of colorectal cancer include:
This article will cover:
"Adeno" is a prefix meaning gland. "Carcinoma" is a type of cancer that grows in epithelial cells, which line the surfaces inside and outside the body. Adenocarcinomas develop in the lining of the large intestine (colon) or the end of the colon (rectum). They often start in the inner lining and spread to other layers.
There are two less common subtypes of adenocarcinomas:
Most information about colorectal cancer refers to colorectal adenocarcinoma, the most common type. Estimates suggest that 4.1 percent of people may develop colorectal cancer during their life, according to the National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) Program.
Colorectal adenocarcinoma symptoms generally include:
Getting screened for colon cancer may detect the disease before it starts causing symptoms. The American Cancer Society (ACS) and the U.S. Preventive Services Task Force both recommend adults start colon cancer screening at age 45.
Diagnosing colorectal cancer starts with a colonoscopy, which lets doctors see inside the rectum and colon. If signs of colorectal cancer are discovered during a colonoscopy, other tests will follow. A biopsy may be performed, which involves removing a small piece of potentially cancerous tissue (sometimes during a colonoscopy) and analyzing the sample for the presence of cancer. Once a diagnosis is confirmed by a colonoscopy and a biopsy, blood tests and imaging tests, such as computed tomography (CT) scans and magnetic resonance imaging (MRI) scans, may be used to help learn more about the cancer and whether it’s spread.
Common treatment options for colorectal adenocarcinomas include:
Carcinoid tumors develop in nerve cells called neuroendocrine cells, which help regulate hormone production. These tumors are among a group of cancers called neuroendocrine tumors (NETs). Carcinoid tumor cells are slow-growing and may develop in the lungs and/or gastrointestinal tract. They account for about 1 percent of all colorectal cancers and half of all cancers found in the small intestine.
Potential symptoms differ depending on where the tumor grows. A carcinoid tumor in the appendix typically doesn’t cause symptoms, unless it begins to block the pathway from the appendix to the intestine, leading to appendicitis symptoms such as fever, nausea and vomiting.
Tumors in the small intestine or colon may cause stomach cramps and pain, weight loss, tiredness, bloating and other stomach problems. Carcinoid tumors in the rectum may cause pain, bleeding and constipation. In the stomach, carcinoid tumors typically don’t cause symptoms.
Carcinoid tumors also sometimes produce hormones that may lead to various symptoms, depending on the type of hormone. For example, 10 percent of people with these tumors may experience flushing in the face, diarrhea, wheezing and rapid heartbeat due to certain hormone-like substances that are released by the tumor, according to the ACS.
Depending on where they develop, gastrointestinal carcinoid tumors may be discovered in various ways. For example, a tumor in the appendix may be found after it causes appendicitis, and the appendix is removed. Rectal tumors may be detected during routine checkups.
Several tests are used to diagnose carcinoid tumors in the abdominal tract, including blood tests, urine tests, imaging scans, endoscopy and colonoscopy.
Gastrointestinal carcinoid tumor treatment options include:
Other types of rare colorectal cancers combined account for less than 5 percent of all cases:
A type of non-Hodgkin lymphoma, this cancer type develops in the lymphatic system, specifically in cells called lymphocytes. Lymphocytes are a type of white blood cell that helps the body fight infections. Lymphoma may develop in many parts of the body, including the lymph nodes, bone marrow, spleen, thymus and the digestive tract. Primary colorectal lymphomas account for 0.5 percent of all colorectal cancers and about 5 percent of lymphomas. This colorectal cancer type usually develops later in life and is more common in men.
Symptoms may include indigestion, bloating, unexplained weight loss, stomach pain, vomiting, diarrhea and other stomach issues. Diagnosis may involve biopsy and endoscopy.
Treatment options vary but may include:
Gastrointestinal stromal tumors are a rare type of colorectal cancer that forms in special cells found in the lining of the gastrointestinal (GI) tract called interstitial cells of Cajal (ICCs). More than 50 percent of GISTs develop in the stomach. While most other GISTs form in the small intestine, the rectum is the third most common location. GISTs are classified as sarcomas, or cancers that begin in the connective tissues, which include fat, muscle, blood vessels, deep skin tissues, nerves, bones and cartilage.
While estimates are uncertain, about 4,000 to 6,000 cases of GIST are diagnosed in the United States every year, according to the ACS. These tumors tend to take a while to grow large enough to start causing symptoms. However, they may cause bleeding in the gastrointestinal tract. Depending on the location of the tumor, blood may show up in vomit or bowel movements. Over time, slow bleeding may lead to a decrease in the amount of red blood cells, a condition called anemia, which causes fatigue and weakness.
Other potential symptoms include:
The diagnostic process may involve an endoscopy, colonoscopy, biopsy and various imaging tests.
Some smaller GISTs may not need to be treated right away, while others are typically treated with surgery and targeted therapy.
Another form of sarcoma, leiomyosarcoma essentially means “cancer of smooth muscle.” The colon and rectum have three layers of the type of muscle affected by leiomyosarcoma, and all three work together to guide waste through the digestive tract. This rare type of colorectal cancer accounts for about 0.1 percent of all colorectal cases.
In the early stages, leiomyosarcomas in the colon or rectum may not cause symptoms. As the cancer progresses, symptoms may include fatigue, weight loss, vomiting blood, changes in stools and other stomach problems. Diagnosis generally includes standard measures, such as a biopsy, blood tests and imaging tests. Treatment typically starts with surgery to remove the tumor. Other treatment options include radiation therapy and chemotherapy.
Most commonly associated with skin cancer, these may start to develop anywhere, including in the colon or rectum, or may spread to the GI tract from the primary melanoma site. Melanomas account for 1 percent to 3 percent of all cancers that develop in the digestive system, according to research published in BMJ Case Reports. How melanomas develop in the colon isn’t well understood, as it’s extremely rare. Diagnosis may involve a biopsy and other tests to determine whether the cancer spread from elsewhere in the body or started in the colon or rectum.
Colorectal melanoma treatment may include:
This cancer, also known as SCC, is extremely rare in the colon, with fewer than 100 cases reported in the literature as of a 2017 case report in the Journal of Community Hospital Internal Medicine Perspectives. Squamous cell carcinoma is typically associated with skin cancer—it’s the second most common type of skin cancer. Squamous cells are a particular type of cell present in many areas of the body. Squamous cell carcinoma occurs when these cells start growing uncontrollably and become cancerous. The reason why this rarely occurs in the colon and rectum isn’t well understood.
Symptoms may resemble colorectal adenocarcinoma, including stomach issues and changes in stool or bowel habits. Colonoscopy and other tests are used to diagnose this cancer. It’s important to determine whether the cancer started in the colon or rectum, or whether it spread to this region from another area of the body. Treatment isn’t standardized but may include surgery, chemotherapy and radiation therapy.
This accounts for about 1 percent of all cancers in the colon or rectum, according to the ACS. People with this syndrome may develop hundreds or even thousands of colon or rectal polyps. These polyps tend to occur when people with this syndrome are 10 to 12 years old. Nearly all people with FAP develop colorectal cancer during their lifetime, and as a result, some people have their colon removed as a preventative measure.
If an inherited syndrome associated with colorectal cancer is suspected, the patient may consider undergoing genetic testing. Genetic testing involves taking a sample of blood, hair or other bodily fluids to analyze for DNA mutations linked to cancer or a genetic syndrome. The patient also may be advised to get regular colonoscopies to look for colorectal cancer and to begin screening early.
Peutz-Jeghers syndrome (PJS): This condition causes a particular type of polyp to develop in the gastrointestinal tract, called a hamartoma. This syndrome is inherited from one’s parents and is caused by mutations in a particular gene (STK11). It comes with an increased risk of colorectal cancer and others including breast cancer, ovarian cancer and pancreatic cancer. If colorectal cancer does occur in individuals with PJS, it tends to develop at a younger than average age.
Familial colorectal cancer: Some people inherit genetic syndromes from their parents that increase their risk of getting colorectal cancer. These syndromes come with mutations—in particular, genes that make it more likely that cancer will develop. Examples include Lynch syndrome, familial adenomatous polyposis and other rarer syndromes. Lynch syndrome is associated with about 2 percent to 4 percent of all cancers in the colon or rectum, according to the ACS. People with Lynch syndrome have a high risk of getting colorectal cancer at some point in their lifetime—up to 50 percent. Those who have Lynch syndrome and go on to develop colorectal cancer tend to get the cancer at an earlier than average age.