The risk factors mentioned above leave the individual susceptible to developing colon or rectal cancers.

Polyps: In the colon and rectum, the exaggerated growth of cells may cause precancerous polyps (adenomas, or adenomatous polyps), which form in the lining of the intestine. Over a period of time some of these polyps may become cancerous. In the later stages of the disease, these cancerous polyps may penetrate the colon walls and metastasize (spread) to nearby lymph nodes and other organs.

Detection of early colon cancer is difficult due to a lack of symptoms. Most colon cancers develop from adenomatous polyps, which is why screening is extremely important for detecting polyps early. Symptoms usually appear with a more advanced disease.

Digital rectal exam: Digital rectal exams are performed in a doctor's office. A gloved finger is used to check the first few inches of the rectum for large polyps and cancers. Although safe and painless, the exam is limited to the lower rectum and cannot detect problems with the upper rectum and colon. In addition, it's difficult for a doctor to feel small polyps.

Fecal occult (hidden) blood test: This test checks a sample of the stool for blood. It can be performed in the doctor's office, or a kit may be given to the patient that explains how to take the sample at home. In colorectal cancer most polyps don't bleed, which can result in a negative stool test result, even though an individual may have cancer. Blood may also be the result of hemorrhoids or minor tears, so it can only aide in the diagnosis of colorectal cancer.

Flexible sigmoidoscopy: The doctor uses a flexible, slender and lighted tube to examine the rectum and sigmoid colon (approximately the last two feet of the colon). The test is fast but can sometimes be uncomfortable. If a polyp or colon cancer is found during this exam, the doctor will recommend a colonoscopy to look at the entire colon and remove any polyps for further examination under a microscope.

Barium enema: This diagnostic test allows the doctor to evaluate the entire large intestine with an X-ray. Barium, a contrast dye, is placed into the bowel using an enema, and air may also be added. The barium fills and coats the lining of the bowel, creating a clear outline of the rectum, colon, and occasionally a small portion of the small intestine. A flexible sigmoidoscopy is often done in addition to the barium enema to aid in detecting small polyps that a barium enema X-ray may miss. This commonly occurs in the lower bowel and rectum.

Colonoscopy: This procedure is the most sensitive test for colon cancer, rectal cancer, and polyps. Colonoscopies are similar to flexible sigmoidoscopies, but the instrument used is a colonoscope, a long, flexible, and slender tube attached to a video camera and monitor. This allows the doctor to view the entire colon and rectum. If any polyps are found during the exam, the doctor may remove them immediately or take tissue samples (biopsies) for analysis. This is done through the colonoscope and is virtually painless, but the patient may receive a mild sedative for comfort. Preparation for the procedure involves drinking a large amount of fluid containing a laxative to clean out the colon.

Genetic testing: If there is a family history of colorectal cancer, the individual may be a candidate for genetic testing.

Blood tests: Blood tests may include a test for anemia (if bleeding occurs). A newer test checks a stool sample for DNA of abnormal cells. It is called the carcinoembryonic antigen (CEA) assay. It is useful because CEA is released into the bloodstream from both cancer cells and normal cells, and has been found in colon cancer.

Biopsy: For a biopsy, the doctor removes a small piece of tissue that is sent to the lab and examined under the microscope to see if any cancer is present.

Ultrasound: Ultrasound uses sound waves to produce a picture of the inside of the body. Two special types of ultrasound may be useful for people with colon or rectal cancer. In one, the instrument that gives off sound waves is placed into the rectum. In the other test, the instrument is used during surgery and is placed against the surface of the liver to see if the cancer has spread there.

CT scan (computed tomography): A CT scan uses x-rays to take many pictures of the body and then combines the pictures by computer which provides a detailed picture. A CT scan can often show whether the cancer has spread to the liver, lungs, or other organs. CT scans can also be used to help guide a biopsy needle into a tumor. A newer way to use a CT scan is to perform a "virtual colonoscopy." Once the colon is cleaned and filled with air, a computer puts together a picture of the inside of the colon. The same preparation for a colonoscopy is used and there may be some discomfort from the bowel being filled with air. If anything abnormal is detected, a follow-up colonoscopy will be needed.

MRI (magnetic resonance imaging): Similar to CT scans, MRI's display a cross-section of the body using radio waves and strong magnets instead of radiation. A contrast dye may be injected, although it is used less often with MRI's. An MRI scan is most helpful when looking at the brain and spinal cord. They may take longer than CT scans, and the patient is placed inside a confining tube.

Chest x-ray: This test may be done to see whether colorectal cancer has spread to the lungs.

PET scan (positron emission tomography): PET scans for colon cancer use a type of radioactive sugar, because cancer cells absorb high amounts of sugar. A special camera is used to visualize where the cancerous cells may reside.

Angiography: A dye is injected and a series of x-ray pictures are taken during this procedure. Surgeons may use this method to find blood vessels near cancers that have spread to the liver.

American Cancer Society Colorectal Cancer Screening Guidelines state that beginning at age 50, both men and women with an average risk should follow one of the five screening options including: yearly stool blood tests, flexible sigmoidoscopy every five years, yearly stool blood test plus flexible sigmoidoscopy every five years, a double contrast barium enema every five years, or a colonoscopy every ten years.

Despite its high incidence, colorectal cancer is one of the most detectable and, if found early enough, most treatable forms of cancer. Over 90% of those diagnosed when the cancer remains localized survive more than five years. However, currently only 37% of colorectal cancers are detected while still localized.

Staging colon cancer: Once diagnosed with colorectal cancer, a doctor will determine the "stage" of the cancer. Staging helps determine how well the individual will do and what treatments are most appropriate.

Stage 0: Stage 0 cancer is the earliest stage. The cancer hasn't grown beyond the inner layer (mucosa) of the colon or rectum. This stage is also known as carcinoma in situ.

Stage I: In stage I, the cancer has grown through the mucosa, but hasn't spread beyond the colon wall or rectum.

Stage II: In stage II, the cancer has grown through the wall of the colon or rectum, but hasn't spread to nearby lymph nodes.

Stage III: In stage III, the cancer has invaded nearby lymph nodes, but isn't affecting other parts of the body.

Stage IV: In stage IV, the cancer has spread to distant sites such as the liver, lung, membrane lining of the abdominal cavity, or to the ovaries.

Recurrent: Recurrent colon cancer may happen following treatment occurring in the colon, rectum, or other parts of the body.

There may be no symptoms in the early stages of the disease. When symptoms appear, they'll likely vary, depending on the cancer's size and location in the large intestine. In some cases, symptoms may result from a condition other than cancer, such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), Crohn's disease, and sometimes diverticulosis or diverticulitis (conditions in which pouches form in the colon wall, weakening it and causing inflammation). Like colorectal cancer, these conditions are treatable.

Signs and symptoms to be aware of include a change in bowel habits including: diarrhea, constipation, a change in the consistency of the stool for more than a couple of weeks, narrow stools, rectal bleeding or blood in the stool, persistent abdominal discomfort such as cramps, gas or pain, abdominal pain with a bowel movement, a feeling that the bowel is not emptying completely, and/or an unexplained weight loss.

Blood in the stool may be a sign of cancer, but it can also indicate other conditions. Bright red blood on bathroom tissue or in the toilet may come from hemorrhoids or minor tears (fissures) in the anus, or from certain foods such as beets, spinach, red cabbage, or food dyes. Iron supplements and some anti-diarrheal medications may make stools appear black.

Metastasis (spreading) to other organs, such as the liver, pancreas, lungs, and lymph nodes may occur causing an increase chance of death.

Colonoscopy procedures may cause complications including perforation (a hole), bleeding, infection, abdominal distension (bloating), postpolypectomy coagulation syndrome (damage to the colon wall from a snare loop or hot forceps used in diagnostic procedures), splenic rupture, and small bowel obstruction.

Age: The chances of having colorectal cancer increases after the age of 50. More than 9 out of 10 people have colorectal cancer when they are over the age of 50.

Previous colorectal cancer: Although the colorectal cancer has been completely removed, there is a risk that new cancers could grow in other areas of the colon and rectum.

History of polyps: An increased risk for colorectal cancer may depend on a larger size or greater number of polyps..

Inflammatory intestinal conditions: Inflammatory bowel diseases such as ulcerative colitis and Crohn's disease increase the risk of colon cancer. In these conditions, the colon is inflamed over a long period of time and there may be ulcers in the lining.

Family history of colorectal cancer: If an individual has close relatives (such as a parent or sibling) that have had colon cancer, their risk is increased. This is especially true if the family member had cancer before the age 60. Individuals with a family history of colorectal cancer should talk to their doctors about how often screening tests should be performed.

Ethnic background: Jewish individuals of Eastern European descent (Ashkenazi) have a higher rate of colon cancer.

Diet: A diet high in fat, especially from animal sources, may increase the risk of colorectal cancer. Poor food choices may result in a deficiency of nutrients, such as calcium, magnesium, pyridoxine (vitamin B6) and folic acid, and these nutrients may be helpful in reducing the risk of colorectal cancer.

Lack of exercise: People who are inactive have a higher risk of colorectal cancer.

Overweight: Obesity increases an individual's risk for colorectal cancer.

Smoking: Recent studies have shown that smokers are 30-40% more likely than nonsmokers to die of colorectal cancer.

Alcohol: Heavy and chronic use of alcohol has been linked to colorectal cancer.

Diabetes: Individuals with diabetes have as a high as a 40% increased risk of developing colorectal cancer.

Other cancers and their treatment: A recent report on testicular cancer survivors found that men with this condition had a higher rate of colorectal cancer. Men who receive radiation therapy for prostate cancer have also been reported to have a higher risk of rectal cancer.