Colon and rectal cancers - InDepth


Colorectal Cancer Screening Guidelines

A number of major organizations, including The American Cancer Society (ACS), The U.S. Preventive Services Task Force (USPSTF), the American College of Physicians, and The American College of Gastroenterology (ACG), have developed guidelines related to screening for colorectal cancer. While there are some differences among these guidelines, they generally recommend that adults ages 45 to 75 who are at average risk for colorectal cancer should be screened with one of these methods:

Stool DNA Test Approved

Cologuard is a stool DNA screening test for colorectal cancer. The home-based test uses a stool sample to check for the presence of blood and DNA changes that may indicate cancer.


Cancers of the colon and rectum, often collectively referred to as colorectal cancer, are tumors that develop in the large intestine.

More than 90% of colorectal tumors develop from a type of polyp called adenomatous polyps. There are many types of polyps. They are common, mostly non-cancerous (benign) tumors. Adenomatous polyps, also called adenomas, are a specific type of polyp that has a greater likelihood of changing into cancer. Because of this risk, adenomas are considered precancerous.

Adenomas are gland-like growths that develop on the lining of the large intestine. They are usually either:

When adenomas become malignant (cancerous), they are referred to as adenocarcinomas. Adenocarcinomas are cancers that originate in glandular tissue cells. Adenocarcinoma is the most common type of colorectal cancer.

The Gastrointestinal Tract

Digestion takes place in the gastrointestinal (GI) tract, which is basically a long tube that extends from the mouth to the anus. It is a complex organ system that first carries food from the mouth down the esophagus to the stomach. Food then travels through the small and large intestines before being excreted through the rectum and out the anus.

Digestive system

The esophagus, stomach, and large and small intestine, aided by the liver, gallbladder, and pancreas, convert the nutritive components of food into energy and break down the non-nutritive components into waste to be excreted.


The esophagus is a narrow muscular tube, about 9 1/2 inches long, that begins below the tongue and ends at the stomach.


In the stomach, acids and stomach motion break food down into particles small enough so that the small intestine can absorb nutrients.


Click the icon to see an image of stomach anatomy.

Small Intestine

The small intestine, despite its name, is the longest part of the gastrointestinal tract. It extends from the stomach to the large intestine and is about 20 feet long. Food passes from the stomach through the small intestine's three parts: first the duodenum, then the jejunum, and finally the ileum. Most of the digestive process occurs in the small intestine.

Small intestine

Click the icon to see an image of small intestine anatomy.

Large Intestine (Colon)

Undigested material, such as plant fiber, is passed next to the large intestine, or colon, mostly in liquid form. The colon is wider than the small intestine but only about 6 feet long. The colon absorbs excess water into the blood. The remaining waste matter is converted to feces through bacterial action. The colon is a continuous structure but it is characterized as having several components.

Cecum and Appendix

The cecum is the first part of the colon after the small intestine. The appendix is attached to the cecum. These structures are located in the lower-right part of the abdomen. The colon continues onward in several sections:

Large intestine (colon)

Click the icon to see an image of large intestine anatomy.

Rectum and Anus

Feces are stored in the descending and sigmoid colon until they are passed through the rectum and anus. The rectum extends through the pelvis from the end of the sigmoid colon to the anus.


In most cases of colon or rectal cancers, the cause or causes are unknown. Defects in genes that normally protect against cancer play the major role in causing polyp cells to change and become cancerous.

Sometimes these cancerous changes are caused by inherited genetic defects and are associated with family histories of colorectal cancer. However, most of the genetic mutations involved in colon cancers appear to arise spontaneously rather than being inherited. In such cases, environmental or other factors may trigger genetic changes in the intestine that lead to cancer.

Risk Factors and Prevention

The American Cancer Society estimates that 101, 420 new cases of colon cancer and 44,180 new cases of rectal cancer will be diagnosed in the United States in 2019.

Rates of colorectal cancer have been decreasing in the United States. This may be due to more people getting regular screenings for colorectal cancer, and fewer people engaging in risk factors, such as smoking. However, many people age 50 years and older still do not receive their recommended screenings.


Colorectal cancer risk increases with age. More than 90% of these cancers occur in people over age 50 years.


Men have a slightly higher risk than women for developing colorectal cancer.

Race and Ethnicity

African-Americans have the highest risk of being diagnosed with, and dying from, colorectal cancer. Among Caucasians, Jews of Eastern European (Ashkenazi) descent have a higher rate of colorectal cancer. Asian Americans/Pacific Islanders, Hispanics/Latinos, and American Indians/Alaska Natives have a lower risk than Caucasians.

Family History of Colorectal Cancer

About 20% to 25% of colorectal cancers occur among people with a family history of the disease. People who have more than one first-degree relative (sibling or parent) with the disease are especially at high risk. The risk is even higher if the relative was diagnosed with colorectal cancer before the age of 60.

A small percentage of people with colorectal cancer have an inherited genetic abnormality that is associated with an increased risk for the disease. The most commonly associated inherited colorectal cancer syndromes associated with genetic mutations include familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC).

Lifestyle Factors

Colon cancer is more common in developed nations than less developed countries. "Western" lifestyle factors are most likely the reason. Diets high in red and processed meats, lack of physical activity, excess weight, and smoking are all associated with an increased risk for colorectal cancer.

Dietary Factors

A diet high in red and processed meats increases the risk for colorectal cancer. Diets high in fruits and vegetables may help reduce risk. The evidence is mixed on whether high intake of dietary fiber is protective. It is also not clear whether there is an association between colorectal cancer risk and deficiencies of folic acid. In any case, neither folic acid nor fiber supplements appear to lower the risk for colorectal cancer. The best sources for dietary fiber and vitamins are fruits, vegetables, nuts, and whole grains.

Alcohol and Smoking

Excessive alcohol use and long-term smoking increase the risk for colorectal cancer.


Obesity is associated with an increased risk for colorectal cancer, especially for men.

Physical Inactivity

A sedentary lifestyle increases the risk of developing colorectal cancer. Regular exercise may help reduce risk.

Medical Conditions That Increase Colorectal Cancer Risk

Adenomatous Polyps (Adenomas)

People who have had adenomas have an increased risk of developing colorectal cancer. When these polyps are detected during a colonoscopy or sigmoidoscopy they can be removed before they turn cancerous.

Inflammatory Bowel Disease (IBD)

IBDs include Crohn disease and ulcerative colitis. The long-term inflammation caused by these chronic disorders can increase the risk for colorectal cancer. IBD is different from irritable bowel syndrome (IBS), which does not increase colorectal cancer risk.


Many studies have identified an association between type 2 diabetes and colon cancer. Both diseases share the common risk factors of obesity and physical inactivity, but diabetes itself is a risk factor for colorectal cancer.

Preventive Factors

Colorectal cancer screenings are a very important preventive measure. Healthy lifestyle measures are also important. For people with certain types of colorectal cancer risk factors, preventive medications may be helpful.

Lifestyle Changes and Prevention

The best way to prevent colorectal cancer is to engage in a healthy lifestyle, which include:

Medications and Prevention

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used pain relievers that include aspirin, ibuprofen (Advil, Motrin, generic), naproxen (Aleve, generic), and the COX-2 inhibitor celecoxib (Celebrex).


It is common to have colon or rectal cancer without symptoms. Many people are free of symptoms until their tumors are quite advanced.

Symptoms associated with colorectal cancer may also be caused by other conditions. These symptoms include:

Diagnosis and Screening

Colon and rectal cancers can be detected early using the screening tests discussed below. These tests can find precancerous polyps and colorectal cancers at stages early enough for complete removal and cure.

Colorectal Cancer Screening Guidelines

The American Cancer Society (ACS), the U.S. Preventive Services Task Force (USPSTF), the American College of Physicians, and the American College of Gastroenterology (ACG) all have made similar, although not identical, recommendations concerning screening for colorectal cancer.

Discuss with your health care provider whether you are at average- or high-risk for colorectal cancer, and which screening test and schedule is most appropriate for you. (See descriptions of screening tests below for more information about the individual tests.)

Screening for Adults with Average Risk for Colorectal Cancer

General age recommendations for colorectal cancer screening are:

Several options and schedules for screening are recommended. The choices include:

Stool tests are another approved way to screen for colon cancer. Several options are available:

If a stool test shows an abnormal result, a colonoscopy is required

Screening for Adults at High-Risk for Colorectal Cancer

People at high risk for colorectal cancer should undergo colonoscopy for screening. The most important risk factors that may prompt screening before age 50 or frequent screenings are:

People in these high-risk groups who have changes that are identified as precancerous during colonoscopy will likely have their doctors discuss with them the possibility of a preventive (prophylactic) colectomy (removal of the entire colon).

Description of Screening Tests


Colonoscopy allows a doctor to view the entire length of the large intestine using a colonoscope, which is inserted into the rectum and snaked through the intestine. A colonoscope is a long, flexible tube that has a video camera at one end. The doctor views images from the colonoscope on a video display monitor.

The test takes about 30 minutes to perform. If polyps are found, the doctor will remove them. The person is given a sedative prior to the test, which produces a comfortable "twilight" sleep.

In order for the doctor to perform a successful colonoscopy, the colon and rectum must be completely empty. Your doctor will give you instructions for how to prepare during the days preceding the tests, and specific foods and liquids to avoid eating and drinking. The day before the test you will be given a laxative solution to clean out the colon. Many people find this cleansing more unpleasant than the colonoscopy itself.

Colonoscopy is generally a safe procedure. In very rare cases, complications, such as bowel perforation, can occur.

Flexible Sigmoidoscopy

Sigmoidoscopy is similar to colonoscopy but only examines the rectum and the lower 2 feet of the colon. (In contrast, colonoscopy allows the doctor to view the entire colon.) The procedure takes about 10 to 20 minutes, and sedation is optional. Preparation procedures are less demanding than those for colonoscopy.

Double-Contrast Barium Enema (DCBE)

The DCBE test uses an x-ray to image the entire large intestine. The test takes about 30 to 45 minutes, and sedation is not required. Preparations are similar to those for colonoscopy and sigmoidoscopy. For the test, barium sulfate is inserted into the rectum using a small, flexible tube. The colon is then pumped with air to help the barium spread through the colon. If polyps are detected in the x-ray, your doctor may recommend you have a colonoscopy for further investigation and polyp removal.

Virtual Colonoscopy

Virtual colonoscopy, also called CT colonoscopy, uses x-rays delivered by computed tomography (CT) scan to take three-dimensional images of the colon. The test takes only 10 minutes to perform, and does not require sedation. (It does require the same preparations as standard colonoscopy to clean out the colon and bowel.) Air is pumped into the rectum through a small flexible tube. The person is then slid into a CT scanner, which takes rapid images. If polyps are detected, a standard colonoscopy is required.

Fecal Occult Blood Test (FOBT)

A FOBT is a take-home test that uses stool samples to detect hidden (occult) blood in feces. It may detect small amounts of blood in stool from polyps or a tumor, even when stools appear normal. Your doctor will give you a kit with instructions on how to take stool samples and prepare them. Your doctor will also inform you about what medications and foods need to be avoided in the days prior to the test. The test kit and samples are sent to a laboratory and results usually come back in a short time. If blood is found in the stool samples, you will need to have a colonoscopy.

Fecal Immunochemical Test (FIT)

The FIT is a take-home test for hidden (occult) blood. The test is similar to the FOBT, but people do not need to follow medication or dietary restrictions. As with the FOBT, a colonoscopy is recommended if blood is found in the stool.

Stool DNA Test (sDNA)

Like the FIT and the FOBT, the sDNA test is done at home and uses fecal samples. No dietary restrictions or test prep are required. Unlike FIT and FOBT, which require multiple stool samples, the sDNA test uses only one bowel movement. In addition to testing for the presence of blood, this test looks for abnormalities in genetic material associated with cancer or precancerous polyps. If DNA mutations are found, a colonoscopy is needed. The first sDNA test was approved by the FDA in 2014. Medicare will cover the test but some insurance carriers may not pay for the full cost.

Diagnosis of Colorectal Cancer

A doctor makes a diagnosis of colorectal cancer based on results of several types of tests. These tests include:


During a colonoscopy, the doctor can remove a tissue sample, which is sent to a laboratory for testing. A biopsy is the only way to definitively diagnose colorectal cancer.

The tumor may also be tested for biomarkers such as microsatellite instability-high (MSI-H) and mismatch-repair deficient (dMMR). Biomarker testing can help guide the optimal treatment regimen.

Blood Tests

Routine blood testing after a diagnosis of colon cancer is made includes a CBC (complete blood count), LFTs (liver function tests) and a CEA (carcinoembryonic antigen) level.

These tests may help your doctor monitor for recurrences of colon cancer after treatment. By themselves, they cannot diagnose cancer and are not used as screening tests.

Imaging Tests

Various types of imaging tests can help detect the presence of cancer or find out how far the cancer has spread. These tests include:


A diagnosis of cancer will lead to staging and other tests to help determine the outlook and the appropriate treatments. Treatment for colorectal cancer can include surgery, chemotherapy, radiation or a combination of these methods.

Colorectal Cancer Stages and Treatment Options

There are several methods for staging colorectal cancer. An older system, known as Dukes', categorizes four basic stages: A, B, C, and D. The current TMN system characterizes the primary tumor (T stage), the lymph node status (N stage), and whether or not the cancer has spread or metastasized (M stage). The results of TMN are combined to determine the stage of the cancer (typically, stage I, II, III, or IV). The stage correlates with the type of treatment recommended as well as the overall prognosis.

Colorectal cancer stages and treatment options are:

Stage 0 (Carcinoma in situ)

Stage I

Stage II

Stage III

Stage IV


Colorectal cancer is among the most curable of cancers when it is caught in its early stages. The term "5-year survival" means that people have lived at least 5 years since diagnosis. The 5-year survival rate for colon cancer diagnosed and treated at stage I is 90%. The rates fall to 70% for stage II and stage III, and 12% for stage IV. However, there are other factors besides stage that can affect a person's prognosis.

Follow-Up Care

After cancer treatment concludes, follow-up care is important to detect any signs of cancer recurrence. The American Society of Clinical Oncology (ASCO) has follow-up care guidelines for people treated for stage II or stage III colorectal cancer. Stage I cancer is less likely to recur. The guidelines recommend:

Healthy Lifestyle

Be sure to follow measures to promote good health. This includes:


In the earliest stages of colorectal cancer (stage 0 and some stage I cases) polyps can be removed during a colonoscopy in a procedure called a polypectomy. Early-stage superficial cancers that are not deep can also be removed through excision during colonoscopy. Unlike colectomy, these procedures do not involve cutting through the abdominal wall.

Surgical removal of the tumor (resection) is the standard initial treatment for potentially curable colorectal cancers (cancers that have not spread beyond the colon or lymph nodes).


Unless colon cancer is very advanced, most tumors are removed by an operation known as colectomy:

Colon cancer - Series

Click the icon to see an illustrated series detailing colon cancer treatment.

The Surgical Approach

The standard technique for a colectomy is open, invasive surgery. Laparoscopy, sometimes called "keyhole surgery," is a newer, and less invasive, method:

Recuperation and Side Effects

After a colectomy, you will need to stay in the hospital until you regain normal bowel function and can eat and drink normally. The hospital stay is usually about 4 to 7 days. You will first be on a liquid diet followed by soft, low-fiber foods and eventually normal foods. There are usually no dietary restrictions after recovery.

Any abdominal surgery may be associated with post operative fatigue and weakness. Daily short walks with increasing distances are encouraged. It may take 4 to 6 weeks for full recovery.

Pelvic laparoscopy

Click the icon to see an image detailing pelvic laparoscopy.
Large bowel resection - Series

Click the icon to see an illustrated series detailing a resection of the large intestine.


A colostomy or ileostomy is performed to bypass the colon and rectum. Colostomy is a surgical procedure that brings one end of the large intestine out through the abdominal wall. (An ileostomy brings the small intestines to the abdominal wall.) The surgeon creates a passage, called a stoma, through the abdominal wall that is connected to the colon.

Feces and gas moving through the intestine pass through the stoma and drain into a special colostomy bag (ostomy pouch) that is attached to the stoma. The bag needs to be emptied several times a day. You will be taught how to keep the area around the stoma clean so as to avoid infection.

The colostomy may be temporary and reversed by a second operation after about 3 to 6 months. If the rectum and sphincter muscles in the rectum need to be removed, the colostomy is typically permanent. The need for colostomies (especially permanent ones) is higher after surgery for rectal cancer than for colon cancer.

Colostomy - Series

Click the icon to see an illustrated series detailing a colostomy procedure.

Surgical Treatments for Rectal Cancer

Surgical treatments for cancer in the rectum are complex since they involve muscles and tissue that are critical for urinary, bowel, and sexual function.

As with colon cancer, early-stage tumors may be removed through local excision or polypectomy. Surgery for more advanced cancers involves cutting away the diseased part of the rectum (rectal resection, also known as proctectomy.)

After rectal resection, the surgeon will perform either an:

Depending on the extent and location of the cancer, other surgical procedures may be performed. In rare cases, if the cancer has spread beyond the rectum to nearby organs, a pelvic exenteration may be required. This involves removal of the rectum, anus, bladder, and urethra as well as male prostate or female reproductive organs.


Chemotherapy Drugs and Regimens

Chemotherapy drugs used for colorectal cancer treatment are:

Many of these drugs are given in combination with each other. Common chemotherapy combination regimens include:

Side effects occur with all chemotherapy drugs and can usually be treated with other medications. Side effects are more severe with higher doses and increase over the course of treatment. Because cancer cells grow and divide rapidly, chemotherapy drugs work by killing fast-growing cells. This means that healthy cells that multiply quickly can also be affected.

Nausea, vomiting, and fatigue are very common side effects. Other side effects can vary depending on the drug used:

Targeted Therapies

Targeted therapies work on a molecular level by blocking specific mechanisms associated with cancer cell growth, division, and survival. Traditional chemotherapy drugs can be effective, but because they do not distinguish between healthy and cancerous cells, their generalized toxicity can cause very severe side effects. The drugs used in targeted therapy also cause side effects, but they tend to be less severe in many but not all cases. Targeted therapies have led to longer survivorship in many cases beyond that of chemotherapy.

Targeted biologic antibody drugs approved for colorectal cancer are:

A drug targeting tumor cell machinery approved for colorectal cancer is:

Drugs targeting the immune system that are approved for colorectal cancer are:


Radiation therapy is used more often for rectal cancer than for colon cancer.

Radiation Therapy for Colon Cancer

Radiation therapy is not a common treatment for colon cancer. The main use for radiation therapy in people with colon cancer is when the cancer has attached to an internal organ or the lining of the abdomen. When this occurs radiation therapy may be used after surgery (adjuvant radiation) to kill any cancer cells that may still remain.

Radiation Therapy for Rectal Cancer

For rectal cancer, radiation therapy is given for various situations:

Types of Radiation Therapy

Radiation therapy uses external or internal sources of radiation to kill cancer cells:

Side Effects of Radiation Therapy

Side effects of radiation may include:



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Review Date: 9/2/2019
Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 08/02/2021.
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