Colorectal cancer by definition is any malignancy occurring as a primary site in the ascending, transverse, or descending colon including the sigmoid and rectal ampulla. Many statistics are available and continue to be collected regarding this frequently occurring and fatal, yet curable, disease. This seemingly contradictory description is nonetheless true, because increased public awareness programs, aggressive screening recommendations, and early diagnosis render this a potentially highly curable disease.
Colorectal cancer is the third most common cancer in the United States and is second only to lung cancer as a cause of cancer death. Worldwide, colorectal cancer is the fourth leading cause of cancer death. In the United States, a person has approximately a 6 percent lifetime chance of developing colorectal cancer, but studies show that the frequency of occurrence and death increase with advancing age. Ninety percent of newly diagnosed colorectal cancers and 94 percent of all colorectal cancer deaths occur in patients over the age of 50. For 2006, 148,610 new cases of colorectal cancer are estimated (72,800 males and 75,810 females). Additionally, 55,170 deaths due to colorectal cancer are predicted in 2006 (27,870 males and 27,300 females). This represents approximately 10 percent of all cancer deaths. Historically, men have had a 35 percent higher rate in occurrence rate and death as compared to women. Furthermore, between the ages of 60 and 79, men have 60 times greater chance and women have 48 times greater chance of developing colorectal cancer as compared to the population younger than 39 years of age.
Racial and ethnic differences are noted both in occurrence and mortality rates. For instance, African-American males have the highest rate of incidence and mortality (72.9 and 34.3 per 100,000 respectively) as compared to non-Hispanic white males (63.1 and 24.8 per 100,000 respectively). In the United States, the incidence of colorectal cancer has slowly decreased, beginning in 1998, but the incidence rate for occurrence in the ascending colon (right-sided colorectal cancer) has increased. Early screening and early polypectomy may be, in part, responsible for this shift.
Familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC) are the two most common forms of inherited familial colorectal cancer syndromes, but they only represent 5 percent of the total new cases each year. FAP, in its various forms, is characterized by an inherited tendency to develop multiple (sometimes hundreds) of colonic polyps of an adenomatous histology. In the most common subtype of FAP, 90 percent of untreated patients will develop colorectal cancer by age 45. In HNPCC (which is actually more common than FAP) individuals develop colon cancer as young as 20 years old, with the average age of diagnosis being 48 years of age. Most (70 percent) of the cancers occur proximal to the splenic flexure and some 10 percent of the cases have synchronous cancers separated by normal bowel. Sporadic cancers are thought to develop from adenomatous polyps. It is noted that if there is a family history of adenomatous polyps then this confers the same risk to the individual as if there were a family history of colorectal cancer.
Inflammatory bowel disease, specifically ulcerative colitis (UC), is another risk factor in development of colorectal cancer. If UC involves the entire large bowel, there is as much as 15 times the risk (compared to the general population) of developing colon cancer and if UC is restricted to the left side (descending colon) the risk is three times that of the general population. Inflammatory bowel disease restricted to the rectum does not appear to increase the risk of developing colorectal cancer. For individuals who have had UC for 10 to 20 years, there is an approximate occurrence of colorectal cancer of about 0.5 percent per year and a 1 percent per year colorectal cancer occurrence after 20 years of the presence of UC. After 40 years of UC, which affects the entire colon (pancolitis), the probability of developing colorectal cancer is approximately 30 percent. Crohn’s disease, which can affect the entire alimentary canal, also shows a similar risk factor in developing colorectal cancer.
Interestingly, type 2 diabetes mellitus and the consequent insulin resistance are risk factors for developing colorectal cancer. Insulin acts as a growth stimulant for colonic mucosal cells and type 2 diabetes and hyperinsulinemia support the increased growth of polyps and colonic tumor cells.
Alcohol increases the risk of developing colorectal cancer when the daily consumption of alcohol exceeds 45 grams. Smoking is a definite risk factor in colorectal cancer occurrence. The American Cancer Society in 2000 estimated that approximately 12 percent of the 1997 deaths from colorectal cancer were due to cigarette smoking. In that review, current male smokers had a 32 percent higher death rate compared to nonsmokers and current female smokers had a 41 percent higher death rate compared to nonsmokers. Furthermore, in that study, the statistics were worse in smokers who had smoked more per day and for more years. These data are from the Cancer Prevention Study II and analyzed statistics on 312,332 men and 469,019 women. A recent study documents that the highest incidence of colorectal cancer is found in individuals who have smoked more than 20 years and who never used nonsteroidal antiinflammatory drugs. Smokers who did use nonsteroidal anti-inflammatory drugs were still at a 30 percent higher risk for developing colorectal cancer, thus showing an incomplete protection against the onset of colorectal cancer. This study was based on the medical history and medical surveillance of 3,299 people between the ages of 20 and 74, half of whom had had colorectal cancer, and the other half had not.
Diet has been an area of intensive study as it relates to colorectal cancer. Since the large bowel (colon) retains the by-products of digestion (and presumably ingested toxins) until elimination (defecation) can occur, it is essential to identify those foods, metabolites and ingested toxins that can predispose an individual to colorectal cancer. Large-scale studies have produced much conflicting data, causing confusion in making recommendations. For instance, high consumption of red meat, animal and saturated fat, and refined carbohydrates (see alcohol) has an increased risk of developing colorectal cancer. Protective effects against colorectal cancer are conferred by consumption of vegetables, fruits, antioxidant vitamins (e.g., vitamins C and E), calcium, and folate.
Dietary fiber was first noted to have a protective effect against colorectal cancer as early as the 1970s and was for many years considered a strong deterrent against colorectal cancer occurrence. A recent prospective study analyzing 725,628 adults indicated that high dietary fiber intake did not reduce the risk of colorectal cancer. This is certainly not in keeping with previous studies and recommendations regarding the colorectal preventative effects of high dietary fiber. The conclusion offered after these data were analyzed was that individuals who ate high levels of dietary fiber also ate less red meat, took antioxidant vitamins, and were more physically active, thus following a more healthy lifestyle. The researchers were equally clear that increased consumption of dietary fiber has proven value in helping to normalize bowel function, control blood sugar in diabetics, and control lipids, thus reaffirming the need for daily dietary fiber intake.
In a five-year study in 2005 of 1,953 patients with colorectal cancer and 2,015 without colorectal cancer, the taking of cholesterol-lowering medications of the statin category was associated with a 47 percent relative reduction of colorectal cancer after adjustment was made for other risk factors. In 2006 a study by the American Cancer Society involving 132,136 patients (men and women) taking statins showed only a weak reduction in the incidence of colorectal cancer and no specific type of statin was found to be more effective than another.
Many methods of screening patients and diagnosing colorectal cancer are available. Screening tests need to be relatively low risk, affordable, and have a reasonable level of security that a positive test is indicative of the presence of the condition and a negative test is indicative that the condition is not present. The fecal occult blood test (FOBT) is a reaction for blood in the stools. This positive reaction is not specific for colorectal cancer, but is based on the presence of blood in the stools (feces) because of intralumenal bleeding, which can occur from partially severed polyps (which could be cancerous) or ulcerating lesions (which may be malignant). For this test to be effective, the patient follows a diet for three days that is restricted in certain foods and medications that may cause a falsely positive reaction from the sample.
The fecal smear is obtained on three separate occasions and the smears are tested by applying an acidic peroxide developer. A positive reaction indicates the presumptive presence of blood and that further workup is indicated, such as flexible sigmoidoscopy (direct examination of the descending colon with a fiberoptic flexible tube) coupled with double-contrast barium enema (radiography of the colon) or full-length colonoscopy. Colonoscopy is a direct visualization through a fiberoptic flexible tube of the entire length of the colon. The advantage of this choice is that if a lesion is seen during the procedure, a biopsy (a piece of the tissue) or complete removal of the abnormal tissue (e.g., polyp, tumor) is accomplished. This allows screening and diagnosis and possibly complete removal of the entire malignancy in one procedure.
Various recommendations for screening populations at risk are available. If individuals have visible blood passage with or between bowel movements, a colonoscopy should be performed to identify the source of bleeding. In general, all men and women with average risk (no personal history or family history of colorectal cancer) should undergo screening for colorectal cancer and adenomatous polyps at 50 years of age. The options for screening are the fecal occult blood test and flexible sigmoidoscopy with double-contrast media (air and barium). In individuals with increased risk, such as personal history of colorectal cancer, ulcerative colitis, Crohn’s disease, and/or adenomatous polyp, a colonoscopy is indicated. Because each of the tests carry some risk to the patient, from not capturing the presence of an abnormal lesion to causing injury to the patient (puncturing the colon, hemorrhaging, infection), the individual and the physician together need to determine the best screening and diagnostic pathway based on the patient’s personal and family medical history, preferences, and the likelihood and ability of the patient to adhere to the mutually agreed upon strategy.
Without question, surgery offers the best potential benefit for a cure of colorectal cancer, especially if the cancer is found early. Surgery by a colonoscopy-directed biopsy includes the complete removal of the cancerous lesion that is contained completely within the colon, and this may be followed by removal of more of the colon through an open abdominal surgery (laparotomy) to insure that tiny portions of cancer (metastasis) in neighboring colonic tissue are removed. Lymph nodes are also removed and examined so that an estimate (staging) of the colorectal cancer can be made.
Spread of the cancer may be to lymph nodes in the area, distant lymph nodes, and other organs, such as the liver and lung. Even if the cancer has spread to the liver (which usually is considered to be incurable by surgery alone), removing a portion of the colon and rerouting the fecal stream may be necessary to prevent painful and life-threatening bowel obstructions from the tumor enlarging inside the bowel. Sometimes, depending on the location of the colorectal cancer in the colon, the remaining end portion of the bowel is brought to the outside of the abdominal wall where the fecal material is captured in a disposable bag (colostomy).
Radiation therapy (the use of intensive X-ray beams to a specific area) is sometimes used to shrink tumors before surgery to help in the removal procedure. Radiation therapy is also used to help shrink tumors that cannot be completely removed. Finally, radiation therapy is directed to colorectal cancer metastases to painful organs, such as the liver and bone, in an effort to help decrease the pain and offer palliative (noncuring comfort) care.
Chemotherapy is used to treat all stages of colorectal cancer. For decades, 5-fluorouracil was the gold standard as the only chemotherapy for colorectal cancer. Now, many new forms of chemotherapy are available and are being investigated to find the best combination and timing for use of these agents.
Because of the prevalence of colorectal cancer, much new research is underway. The best treatment is the individual’s own awareness of the family history and personal bodily function, and early screening for the condition.
Cancer (General); Colonic Diseases (General); Colon Polyps.
19.1 Introduction Colorectal cancer (CRC) is the third leading cause of cancer death worldwide, representing 10% of cancer diagnoses and deaths .
Colon cancer is unregulated cell replication and accumulation in the colon. Colon cancer is often called colorectal cancer. Colorectal cancer...
INCIDENCE Cancer of the colon is an extremely common form of cancer. After the lung, the colon is the most common site of cancer...