Colorectal cancer is one of the most common cancers in the Western world. Many countries have already implemented screening programs or are considering them. Certain requirements must be fulfilled for a screening program to be effective for early detection of disease:
The disease must occur with a certain frequency (high incidence) and be associated with a certain mortality (or morbidity).
There must be a precursor lesion or an early form of the disease that persists over a long period of time (“screening window”).
Techniques must exist (screening methods) that allow these early stages of disease to be identified and treated.
Treatment of the preliminary or early form of the disease must achieve a reduction in the mortality rate associated with the disease (Fig. 6.1).
The screening method must be a low-risk procedure with high compliance in the general population, since it involves supposedly healthy individuals undergoing a procedure that carries the risk of complications.
Colorectal carcinoma is an ideal candidate for screening. To address the five points listed above:
Colorectal carcinoma is one of the most common cancers in the Western world.
Colorectal adenomas are an identifiable benign precursor of colorectal cancer. An adenoma can be present for a relatively long period of time (approx. 10 years) before cancer develops (adenoma–carcinoma sequence). Adenomas are detectable by screening procedures. The incidence of malignant transformation of adenomatous polyps increases with the size of the polyps. The risk of malignancy in polyps smaller than 5 mm is less than 0.01%, for polyps that are 5–9 mm in size it is less than 1%, and for those measuring 10–15 mm it is 1%–5%. The risk that a diminutive polyp (<5 mm) will undergo malignant transformation within the next 10 years is estimated to be approximately 1% (Fig. 6.2).
Colorectal adenomas can be removed by polypectomy during optical colonoscopy.
Studies have shown that endoscopic polypectomy can reduce the risk of developing colorectal carcinoma by 76%–90%.
Colorectal carcinoma thus meets all of the requirements for a screening program to effectively reduce the incidence and mortality of the disease.
Although optical colonoscopy has been made available as a screening method in many industrialized nations for people with health insurance coverage, compliance in the general population is still low. At present, optical colonoscopy is the only truly effective screening procedure available as it allows both detection and removal of polyps in a single session.