Abstract 3242: Colorectal cancer screening pilot: Comparative effectiveness research using two screening modalities

Although several modalities are being used in colorectal cancer (CRC) screening, only fecal occult blood testing (FOBT) and flexible sigmoidoscopy (FS) have been subjected to randomized trials and long-term follow-up. Both have been found to reduce CRC mortality compared to no screening (18% and 28%, respectively), but a direct comparison between the two has never been done with end-point CRC incidence and mortality. Also, it is not clear which modality is the most cost-effective in any given population. In Norway, a country with high colorectal cancer incidence and little prior screening against the disease, the government decided to start a comparative effectiveness research pilot in 2012 with these two screening modalities. The pilot aims to randomize the entire population aged 50-74 in a defined geographical area in South-East Norway (approximately 140 000 individuals) to one of two screening modalities. Half will be randomized to biennial screening with immunochemical FOBT (OC-Sensor Diana, Eiken Ltd), and half to once only screening with FS. The enrollment will take four years and the pilot includes a number of sub-studies to determine how the screening is perceived in the target population. We report the results from the enrollment in the main trial after the first 18 months. A total of 35746 women and men have been invited so far, 21495 to iFOBT and 14251 to FS. Participation rates have been 49% in the FS arm, and 57% in the iFOBT arm, with slightly higher rates among women than men. Positive FS was defined as advanced neoplasia or three or more adenomas. A total of 10.6% of the FS patients have been referred to colonoscopy. The cut-off value for positive iFOBT was set to 75 ug/L, and 780 patients (6.4%) have so far tested positive and referred to colonoscopy. Forty-three cases of CRC have been detected in the FS group so far, at a rate of 6/1000 examined, somewhat higher in men (7.3/1000) than in women (5/1000). Thirty-nine cancers have been found in the FOBT group after first screening round (3.1/1000 examined), with 4.6/1000 in men and 1.9/1000 in women. Overall the adenoma detection rate at sigmoidoscopy is 14%. A total of 881 high-risk adenomas (adenomas >10 mm, or with high-grade dysplasia or villous features) have been detected. Adenoma detection rate at colonoscopy in the referred population is 60.5%. Complications at sigmoidoscopy have so far been 14/1000 exams, with the vast majority being vasovagal. At colonoscopy the complication rate i