Through screening colonoscopy, practitioners can identify and remove cancers and premalignant lesions throughout the colon and rectum, a practice that has been shown to reduce the incidence of colorectal cancer. Furthermore, early diagnosis of cancer lowers mortality from colorectal cancer. Cost-benefit analysis precludes widespread use of colonoscopy as a screening method; and in persons at average risk for colorectal cancer, the US Agency for Health Care Policy and Research recommends colonoscopy every 10 years. However, more frequent screening is warranted in individuals at high risk of developing colorectal cancer. Two indications for screening colonoscopy have recently been described in the literature.
Advanced Histology Warrants Screening
Follow-up colonoscopy is not always necessary for individuals found to have distal colonic tubular adenomas (TAs) at sigmoidoscopy, according to a report in JAMA. Colonoscopy is indicated, however, if a patient has advanced distal histology or is older than 65 years; these factors are associated with an increased risk of advanced proximal neoplasia.
Levin and colleagues performed a cross-sectional analysis over a 2-year period at a large group-model health maintenance organization. After excluding patients with high-risk family history or a history of polyps, the authors included in their analysis 64,204 subjects who had undergone sigmoidoscopy. Of these, 2,972 asymptomatic subjects age 50 years and older underwent colonoscopy as a follow-up to screening sigmoidoscopy.
Using the number and size of adenomas as well as the patient's age, sex, and family history as predictors, the authors discovered a number of criteria that practitioners can use when screening for colonic abnormalities. In multivariate analysis as well as computerized classification and regression tree (CART) analysis, the size of a TA was not related to the risk of proximal neoplasia.
In patients who went on to have a colonoscopy, rates of proximal advanced adenomas and adenocarcinoma were found to be similar in patients without a distal adenoma, and those with adenomas smaller than 1 cm and larger than 1 cm (5.3%, 5.5%, and 5.6%, respectively). However, 12.1% of patients with distal villous or tubulovillous adenomas had advanced proximal neoplasia. In addition, patients age 65 years or older with a positive family history of colorectal cancer and with multiple distal adenomas were also at increased risk.
As an alternative to colonoscopy for colorectal cancer screening, the authors recommend that clinicians continue to screen with sigmoidoscopy starting at age 50 to 55 years for average-risk patients, followed by colonoscopy at age 65 years. Patients who are not in a high-risk category or who are younger than age 65 may not need a follow-up colonoscopy.
Invasive cancer takes many years to develop. Thus, if small proximal lesions are left in place in younger subjects, a colonoscopy at age 65 would likely detect any lesions before they progressed to invasive cancer. However, if there is a high risk of advanced neoplasm, primary screening colonoscopy every 10 years in patients older than age 50 may be warranted.
In their prospective study, the researchers examined colonoscopic findings from 155 patients with acromegaly. Even though only one patient had actual symptoms, colorectal carcinomas were found in eight patients (5%), and at least one tubular adenoma was found in 39 patients (25%). Importantly, three of the cancers were discovered at the cecum, an unusual site to find "sporadic" cancers. Those who had cancers tended to be older, and left-sided tubular adenomas were more prevalent -- especially in individuals older than age 50. The median age when finding carcinoma was 64, but the youngest patient with an adenoma was 39.
Although 55 is considered the age at which sigmoidoscope screening is generally recommended, the authors advise colonoscopic screening beginning at age 40 and every two to three years thereafter for patients with acromegaly. In addition, due to the sites where cancer was detected in the study patients, a total colonoscopy is recommended.
The researchers point out additional, practical issues regarding the success of obtaining adequate colonoscopy in the acromegalic patient. For instance, considering the fact that the colon of a patient with acromegaly is longer and also larger in circumference, an "overtube" is often needed, as is "good colonoscopic technique." Also, one must consider the increased large bowel transit time (up to 37 hours) in the individual with acromegaly. Adjustments in bowel preparation are therefore needed. Finally, reaching the cecum is crucial, and colonoscopy of these patients should be done only by the experienced endoscopist.
The article discusses potential mechanisms for the development of colorectal cancer in acromegalic patients. Several theories are possible, such as the influence of "insulin-like growth factor I, the tissue biomarker of growth hormone," which seems to be elevated in acromegaly. The authors postulate that the development of colorectal carcinoma may be multifactorial and that "local environmental influences" may also play a role. Perhaps one such influence may be from the "unconjugated secondary bile acid, deoxycholic acid."