**2. Epidemiology**

The prevalence of cancerous polyps in series of endoscopically removed polyps is between 0.2% and 11% [4-6].Currently, screening programs allow the detection and treatment of a great number of adenomas and malignant polyps, and this contributes to a reduction of the mortality by colorectal cancer (CRC) [1,7]. In an asymptomatic population of people over 50 years old who underwent direct colonoscopy, there was a 0.8% prevalence of adenocarcino‐ ma of which 50% were carcinoma "in situ" or in stage I [8,9]. During screening programmes, adenocarcinomas have been detected in between 3% - 4.6% of those who undergo colono‐ scopy following a positive immunological faecal occult blood test result [10,11].
