Colorectal cancer is a significant contributor to morbidity and mortality in the U.S., making this disease the second leading cause of cancer deaths overall. In 2002, more than 56,000 lining of the bowel. Some become malignant over time. Most evidence suggests that adenomas are precursors for a substantial proportion of colorectal cancers. This has prompted considerable interest in removing adenomas to prevent the people in the U.S. died of colorectal cancer (28,471 men; 28,132 women). Studies published in the early 1990s showed that screening could reduce colorectal cancer-related mortality; this finding has prompted many organizations to recommend screening in asymptomatic, average-risk adults older than 50 years of age.
The National Health Interview Survey, conducted by the Centers for Disease Control and Prevention (CDC) in 2000, indicated that many people who were at risk for colorectal cancer were not being screened. Although screening rates are beginning to rise, they remain too low to achieve the Department of Health and Human Services’ Healthy People 2010 objective for reducing mortality rates from colorectal cancer. In 2004, approximately 57% of adults aged 50 years or older reported that they received a fecal occult blood test (FOBT) or a lower endoscopy examination within one year of being surveyed by CDC’s Behavioral Risk Factor Surveillance System, compared with 54% of adults surveyed in 2002. buy cialis soft tabs
Colorectal cancer takes approximately equal numbers of lives of both men and women each year. Mortality rates for colorectal cancer have declined for men since 1985 and for women since 1950. This decreased incidence and mortality rate is largely a result of detection and removal of precancerous polyps, early detection of tumors through screening, and improved treatments.
The etiology of colorectal cancer is complex and appears to involve interactions between inherited susceptibility and environmental factors. Most colorectal cancers are thought to develop from benign precursor lesions, or adenomatous polyps, which may vary from tiny nodules to tumors up to 12 cm in diameter. These cancers can arise in a pre-existing adenoma or de novo, but the relative importance of these two pathways is unclear. Colorectal cancer develops from areas of dysplasia.
Adenomas and carcinomas often coexist, and adenomatous remnants are frequently found in carcinomas. De novo cancers, however, have been observed to arise in flat mucosa, and flat elevated cancers may originate from a pathway that differs from the adenoma-carcinoma sequence. Adenomatous polyps are benign tumors that develop on the development of colorectal cancer. Between 70% and 90% of colorectal cancers arise from adenomatous polyps, and 10% to 30% arise from sessile adenomas. The larger the polyp, the greater the potential for malignancy. Viagra Online Canadian Pharmacy
Diminutive polyps (5 mm or less in diameter) have a negligible malignant potential. Polyps with a diameter of 5 to 10 mm are considered small, whereas polyps greater than 10 mm in diameter are considered large. Polyps larger than 2 cm in diameter have a 50% chance of becoming malignant over time.
The American Cancer Society has recommended the following screening protocol for people at normal risk older than 50 years of age:
- a yearly fecal occult blood test to detect microscopic blood in the stool
- flexible sigmoidoscopy at age 50 for direct visualization of the colon lining via a sigmoidoscope or an endoscope
- flexible sigmoidoscopy, repeated every five years
- double-contrast barium enema every five years to show the contour of the lining of the colon; a white contrast image of the lining is visible on x-ray film.
- colonoscopy of the entire colon every 10 years
In 2003, the American Gastroenterological Association revised its screening guidelines as follows:
- People with two or more first-degree relatives with colorectal cancer or a first-degree relative with colon or rectal cancer before age 60 should have a screening colonoscopy beginning at age 40 or beginning 10 years prior to the age of the earlier colon cancer diagnosis in the family (whichever is earliest).
- People with a first-degree relative who had colon cancer after age 60 or with two second-degree relatives who had colon or rectal cancer should begin screening at age 40 with one of the methods listed earlier, such as annual sig-moidoscopy.
The prognosis of patients with colon cancer is related to the degree of penetration of the tumor through the bowel wall, the presence or absence of nodal involvement, and the presence or absence of distant metastases. These three characteristics form the basis for all staging systems developed for this disease. Bowel obstruction and bowel perforation indicate a poor prognosis.
After the diagnosis has been confirmed by biopsy, the pathological stage of the cancer is assigned. Often the depth of penetration through the bowel or the presence of regional lymph nodes cannot be assessed before surgery.
Stages I through IV correspond with Dukes classes A through D, based on these general criteria:
- Stage I: The tumor is confined to the epithelium or has not penetrated through the first layer of muscle in the bowel wall.
- Stage II: The tumor has penetrated through to the outer wall of the colon or has gone through it, possibly invading other local tissue.
- Stage III: A tumor of any depth or size is associated with regional lymph node involvement.
- Stage IV: Any of the previous criteria are associated with distant metastasis.
Although prior staging plays an important role in determining the various options for treating many cancer patients, it is not necessary to ascertain such staging in colon cancer patients.