Prevalence and incidence of colorectal adenomas and cancer in asymptomatic persons.

The prevalence of colorectal adenomatous polyps varies widely from country to country and is highly correlated with colorectal cancer incidence rates in each country. The prevalence of adenomas reported in older studies was based on autopsy findings and is higher than that in more recent studies based on endoscopy findings. Among asymptomatic, average-risk patients, adenoma prevalence averages approximately 10% in sigmoidoscopy studies and more than 25% in colonoscopy studies, whereas the prevalence of colorectal cancer among these patients is less than 1%. The cumulative incidence of new adenomas within 3 years after normal endoscopy averages about 7% by flexible sigmoidoscopy and 27% by colonoscopy.

An overview of adenocarcinoma of the small intestine.

Even though the small intestine contains 90% of the gastrointestinal tract mucosa and is located between the stomach and large intestine, two organs with a high cancer incidence, adenocarcinoma of the small intestine is 1/50th as common as adenocarcinoma of the large bowel. In several other respects, small-intestinal adenocarcinoma resembles large bowel adenocarcinoma; eg, it arises from adenomatous polyps, co-occurs in the same individuals, and has a similar pattern of incidence rates by country. Small-intestinal adenocarcinoma is diagnosed prior to surgery in only about 50% of cases and often occurs in conjunction with small bowel obstruction. The mainstay of treatment is surgery; prognosis depends on stage at presentation. Little is known about the use of radiotherapy and chemotherapy in this malignancy, but most physicians utilize therapeutic strategies modeled on the management of large-intestinal adenocarcinoma. Clarification of the reason for the low incidence of small-intestinal adenocarcinoma could lead to new interventions for the prevention of colorectal cancer.