Colon and rectal cancers develop in the lower gastrointestinal (GI) tract, the system that processes food for energy and rids the body of solid waste matter (fecal matter or stool). Cancer can develop in any part of the colon or rectum and is thought to develop slowly over a period of several years. Before a cancer develops, there usually are precancerous changes in the lining of the colon or rectum, including dysplasia or adenomatous polyps. A polyp is a growth of tissue into the lumen of the colon or rectum. Some types of polyps (hyperplastic polyps and inflammatory polyps) are not precancerous, but having adenomatous polyps (also called adenomas) does increase one’s risk of developing cancer, especially if there are multiple adenomas, if they are over one centimeter in size or if they display abnormal cellular patterns (dysplasia).

In contrast to the growth of an adenoma into the hollow lining of the colon, a cancer can grow inward through the wall of the large bowel. If not treated, cells from the tumor may break away and spread through the bloodstream or lymph system to other parts of the body, where they can form secondary tumors (a process called metastasis).

Over 95% of colorectal cancers are adenocarcinomas — derived from the glandular cells lining the inside of the colon and rectum. Other, rarer types of tumors may also develop in the colon and rectum, including carcinoid tumors (from hormone-producing cells of the intestine), gastrointestinal stromal tumors (from the connective tissue and muscle layers in the colon or rectal wall) and lymphomas (cancers of the immune system and its component cells).

Cancers beginning in different areas of the large bowel may cause different symptoms. Signs and symptoms of colorectal cancer include rectal bleeding, blood in the stool and a change in bowel habits. The cancer can exist for an extended time without symptoms; those detected because of symptoms have usually progressed beyond a localized stage.

Several effective screening tools exist for the early detection of adenomatous polyps and colorectal cancer. Screening with fecal occult blood testing and flexible sigmoidoscopy has been shown to reduce death rates either by detecting and removing polyps before they become malignant, or by detecting and removing early-stage colorectal cancers when still highly curable. The following procedures are currently available for use in colorectal cancer screening:

Digital Rectal Examination (DRE): A simple, painless test during which a physician inserts a lubricated, gloved finger into the rectum to feel for irregular or abnormal areas. Although useful in detecting some polyps and cancers, the DRE is limited to only the rectum area, and should be performed prior to sigmoidoscopy, colonoscopy or double-contrast barium enema. [ 4 ]

Fecal Occult Blood Test (FOBT): Examines samples of stool for the presence of hidden, or “occult,” blood that can be a sign of tumor or polyps in the intestine. Patients receive a test kit to take home along with dietary instructions to follow for several days before beginning the test. The test consists of taking a small stool sample from three consecutive bowel movements and then returning the kit to the doctor’s office or laboratory for evaluation [ 4 ]. Randomized controlled studies have demonstrated the effectiveness of annual or biennial FOBTs in reducing cancer mortality. [ 5 ]

Flexible Sigmoidoscopy: Insertion of a slender, flexible, hollow, lighted tube (sigmoidoscope) into the rectum to view the inside of the rectum and the lower part of the colon (sigmoid) for cancer or polyps. This test may be somewhat uncomfortable, but it is generally not painful. If a polyp or other mass is observed, the patient is referred for colonoscopy to obtain a biopsy, and to observe the remainder of the colon that is not reachable by sigmoidoscope. [ 4 ] Case-control studies have demonstrated a reduction in colon cancers [ 5 ] within the distal colon (within reach of the instrument).

Colonoscopy: Insertion of a long, flexible, hollow, lighted tube, similar to a sigmoidoscope, through the rectum, to examine the entire colon. The colonoscope is connected to a video camera that allows the physician to view closely the inside of the colon. If a polyp is found, it can be removed immediately by passing a wire loop through the colonoscope and cutting the polyp from the wall of the colon with an electrical current. Colonoscopy requires more extensive preparation than does sigmoidoscopy, usually including sedation during the examination. [ 4 ] While comparative studies suggest a reduction in colorectal cancer incidence after colonoscopy, a randomized controlled trial has just begun. [ 6 ]

Barium Enema with Air Contrast (also called Double-Contrast Barium Enema): An enema of barium sulfate is given through the rectum to partially fill and open the colon. The barium sulfate spreads throughout the colon and then most of it is removed. The colon is partially inflated with air, expanding it and increasing the contrast and quality of x-rays. [ 4 ]

New technologies hold promise for the design of colorectal cancer screening tests with acceptable sensitivity and specificity that are minimally invasive and relatively safe. Virtual colonoscopy, a method of imaging the colon in which thin-section, helical computed tomography (CT) is used to generate high-resolution, two-dimensional axial images from which three-dimensional images are then reconstructed off-line, is currently being studied to compare its diagnostic performance with that of conventional colonoscopy, with initial positive results. Although virtual colonoscopy requires full bowel preparation, it takes less time and does not require sedation. [ 7 ] In addition, molecular genetic approaches for colorectal cancer screening that detect DNA mutations in stool have the potential to be very specific and sensitive as well as cost-effective. [ 8 ] Such alternatives to current screening techniques may be more tolerable to patients, thereby increasing their compliance.

Colorectal cancer is highly preventable and, when detected early, eminently curable. The five-year relative survival rate is 90% when it is discovered and treated early. Unfortunately, only 37% of colorectal cancers are found at this early stage. The five-year relative survival rate decreases to 65% after the cancer has spread to nearby organs or lymph nodes, and to only 8% if it has spread to distant parts of the body. [ 9 ]

Surgery is the most common form of therapy for colorectal cancer, and for cancers that have not metastisized, it is frequently curative. Chemotherapy, or chemotherapy plus radiation, is given before or after surgery to most patients whose cancer has deeply perforated the bowel wall or has spread to the lymph nodes. A permanent colostomy — creation of an abdominal opening for elimination of body wastes — is rarely needed for colon cancer and only infrequently for rectal cancer. [ 10 ]

When the cancer cannot be cured, effective symptom control and, if needed, palliative care are appropriate parts of a comprehensive care plan that optimally involves the hospital, the patient’s own physician and inpatient or outpatient hospice.