Colorectal cancer, also called colon cancer or bowel cancer, includes cancerous growths in the colon, rectum and appendix. It is the third most common form of cancer and the second leading cause of cancer-related death in the Western world.

 Colorectal cancer causes 655,000 deaths worldwide per year. Many colorectal cancers are thought to arise from adenomatous polyps in the colon. These mushroom-like growths are usually benign, but some may develop into cancer over time. The majority of the time, the diagnosis of localized colon cancer is through colonoscopy. Therapy is usually through surgery, which in many cases is followed by chemotherapy.

 Symptoms 

Colon cancer often causes no symptoms until it has reached a relatively advanced stage. Thus, many organizations recommend periodic screening for the disease with fecal occult blood testing and colonoscopy. When symptoms do occur, they depend on the site of the lesion. Generally speaking, the nearer the lesion is to the anus, the more bowel symptoms there will be, such as:

     * Change in bowel habits

          o change in frequency (constipation and/or diarrhea),

          o change in the quality of stools

          o change in consistency of stools

    * Bloody stools or rectal bleeding

    * Stools with mucus

    * Tarry stools (melena) (more likely related to upper gastrointestinal eg stomach or duodenal disease)

    * Feeling of incomplete defecation (Tenesmus) (usually associated with rectal cancer)

    * Reduction in diameter of feces

    * Bowel obstruction (rare)

 

Constitutional symptoms

Especially in the cases of cancer in the ascending colon, sometimes only the less specific constitutional symptoms will be found: 

    * Anemia, with symptoms such as dizziness, malaise and palpitations. Clinically there will be pallor and a complete blood picture will confirm the low hemoglobin level.

    * Anorexia

    * Asthenia, weakness

    * Unexplained weight loss.

 Metastatic symptoms

 There may also be symptoms attributed to distant metastasis:

     * Shortness of breath as in lung metastasis

    * Epigastric or right upper quadrant pain, as in liver metastasis. Rarely can there be jaundice if the outflow of bile is blocked. Clinically there might be liver enlargement.

 

 Risk factors

 The lifetime risk of developing colon cancer in the United States is about 7%. Certain factors increase a person's risk of developing the disease. These include:

     * Age. The risk of developing colorectal cancer increases with age. Most cases occur in the 60s and 70s, while cases before age 50 are uncommon unless a family history of early colon cancer is present.

    * Polyps of the colon, particularly adenomatous polyps, are a risk factor for colon cancer. The removal of colon polyps at the time of colonoscopy reduces the subsequent risk of colon cancer.

    * History of cancer. Individuals who have previously been diagnosed and treated for colon cancer are at risk for developing colon cancer in the future. Women who have had cancer of the ovary, uterus, or breast are at higher risk of developing colorectal cancer.

    * Heredity:

          o Family history of colon cancer, especially in a close relative before the age of 55 or multiple relatives

          o Familial adenomatous polyposis (FAP) carries a near 100% risk of developing colorectal cancer by the age of 40 if untreated

          o Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome

    * Long-standing ulcerative colitis or Crohn's disease of the colon, approximately 30% after 25 years if the entire colon is involved

    * Smoking. Smokers are more likely to die of colorectal cancer than non-smokers. An American Cancer Society study found that "Women who smoked were more than 40% more likely to die from colorectal cancer than women who never had smoked. Male smokers had more than a 30% increase in risk of dying from the disease compared to men who never had smoked."

    * Diet. Studies show that a diet high in red meat and low in fresh fruit, vegetables, poultry and fish increases the risk of colorectal cancer. In June 2005, a study by the European Prospective Investigation into Cancer and Nutrition suggested that diets high in red and processed meat, as well as those low in fiber, are associated with an increased risk of colorectal cancer. Individuals who frequently ate fish showed a decreased risk. However, other studies have cast doubt on the claim that diets high in fiber decrease the risk of colorectal cancer; rather, low-fiber diet was associated with other risk factors, leading to confounding. The nature of the relationship between dietary fiber and risk of colorectal cancer remains controversial.

    * Physical inactivity. People who are physically active are at lower risk of developing colorectal cancer.

    * Virus. Exposure to some viruses (such as particular strains of human papilloma virus) may be associated with colorectal cancer.

    * Alcohol. See the subsection below.

    * Primary sclerosing cholangitis offers a risk independent to ulcerative colitis

    * Low selenium.

 

Alcohol

 On its colorectal cancer page, the National Cancer Institute does not list alcohol as a risk factor: however, on another page it states, "Heavy alcohol use may also increase the risk of colorectal cancer"

 The NIAAA reports that, "Epidemiologic studies have found a small but consistent dose-dependent association between alcohol consumption and colorectal cancer even when controlling for fiber and other dietary factors. Despite the large number of studies, however, causality cannot be determined from the available data."

 "Heavy alcohol use may also increase the risk of colorectal cancer" (NCI). One study found that "People who drink more than 30 grams of alcohol per day (and especially those who drink more than 45 grams per day) appear to have a slightly higher risk for colorectal cancer." Another found that "The consumption of one or more alcoholic beverages a day at baseline was associated with approximately a 70% greater risk of colon cancer."

 One study found that "While there was a more than twofold increased risk of significant colorectal neoplasia in people who drink spirits and beer, people who drank wine had a lower risk. In our sample, people who drank more than eight servings of beer or spirits per week had at least a one in five chance of having significant colorectal neoplasia detected by screening colonoscopy."

 Other research suggests that "to minimize your risk of developing colorectal cancer, it's best to drink in moderation"

 Drinking may be a cause of earlier onset of colorectal cancer.

 Diagnosis, screening and monitoring

 Colorectal cancer can take many years to develop and early detection of colorectal cancer greatly improves the chances of a cure. Therefore, screening for the disease is recommended in individuals who are at increased risk. There are several different tests available for this purpose.

     * Digital rectal exam (DRE): The doctor inserts a lubricated, gloved finger into the rectum to feel for abnormal areas. It only detects tumors large enough to be felt in the distal part of the rectum and is not really a screening test.

    * Fecal occult blood test (FOBT): a test for blood in the stool.

    * Endoscopy:

          o Sigmoidoscopy: A lighted probe (sigmoidoscope) is inserted into the rectum and lower colon to check for polyps and other abnormalities.

          o Colonoscopy: A lighted probe called a colonoscope is inserted into the rectum and the entire colon to look for polyps and other abnormalities that may be caused by cancer. A colonoscopy has the advantage that if polyps are found during the procedure they can be immediately removed. Tissue can also be taken for biopsy.

 In the United States, colonoscopy or FOBT plus sigmoidoscopy are the preferred screening options.

 Other screening methods 

    * Double contrast barium enema (DCBE): First, an overnight preparation is taken to cleanse the colon. An enema containing barium sulfate is administered, then air is insufflated into the colon, distending it. The result is a thin layer of barium over the inner lining of the colon which is visible on X-ray films. A cancer or a precancerous polyp can be detected this way. This technique can miss the (less common) flat polyp.

    * Virtual colonoscopy replaces X-ray films in the double contrast barium enema (above) with a special computed tomography scan and requires special workstation software in order for the radiologist to interpret. This technique is approaching colonoscopy in sensitivity for polyps. However, any polyps found must still be removed by standard colonoscopy.

    * Standard computed axial tomography is an x-ray method that can be used to determine the degree of spread of cancer, but is not sensitive enough to use for screening. Some cancers are found in CAT scans performed for other reasons.

    * Blood tests: Measurement of the patient's blood for elevated levels of certain proteins can give an indication of tumor load. In particular, high levels of carcinoembryonic antigen (CEA) in the blood can indicate metastasis of adenocarcinoma. These tests are frequently false positive or false negative, and are not recommended for screening.

    * Genetic counseling and genetic testing for families who may have a hereditary form of colon cancer, such as hereditary nonpolyposis colorectal cancer (HNPCC) or familial adenomatous polyposis (FAP).

    * Positron emission tomography (PET) is a 3-dimensional scanning technology where a radioactive sugar is injected into the patient, the sugar collects in tissues with high metabolic activity, and an image is formed by measuring the emission of radiation from the sugar. Because cancer cells often have very high metabolic rate, this can be used to differentiate benign and malignant tumors. PET is not used for screening and does not (yet) have a place in routine workup of colorectal cancer cases.

    * Whole-Body PET imaging is the most accurate diagnostic test for detection of recurrent colorectal cancer, and is a cost-effective way to differentiate resectable from non-resectable disease. A PET scan is indicated whenever a major management decision depends upon accurate evaluation of tumour presence and extent.

    * Stool DNA testing is an emerging technology in screening for colorectal cancer. Pre-malignant adenomas and cancers shed DNA markers from their cells which are not degraded during the digestive process and remain stable in the stool. Capture, followed by Polymerase Chain Reaction amplifies the DNA to detectable levels for assay. Clinical studies have shown a cancer detection sensitivity of 71%-91%.

 

Pathology

The pathology of the tumor is usually reported from the analysis of tissue taken from a biopsy or surgery. A pathology report will usually contain a description of cell type and grade. The most common colon cancer cell type is adenocarcinoma which accounts for 95% of cases. Other, rarer types include lymphoma and squamous cell carcinoma.

Staging

 Colon cancer staging is an estimate of the amount of penetration of a particular cancer. It is performed for diagnostic and research purposes, and to determine the best method of treatment. The systems for staging colorectal cancers largely depend on the extent of local invasion, the degree of lymph node involvement and whether there is distant metastasis.

 

 

 

 

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