ABSTRACT: Colorectal cancer (CRC) is currently the second most common cause of cancer death in the United States, and one of the most preventable cancers. It has been shown in several randomized controlled trials that screening using fecal occult blood testing (FOBT) reduces CRC mortality by 13-33%. While there is strong consensus amongst experts regarding the value of CRC screening, the best approach to screening is not clear. Of the widely recommended modalities, FOBT and colonoscopy are the most commonly used within the United States. FOBT is inexpensive, non-invasive, and its use as a screening tool is supported by the highest quality evidence (i.e. randomized controlled trials). Moreover, newer FOBT, such as fecal immunochemical tests or FITs, have advantages over conventional FOBT in terms of both test characteristics and ease of use that make them quite attractive as a population-based screening tool.
While colonoscopy is invasive and has higher up-front risks and costs than FOBT, it does afford the opportunity to directly assess the colonic mucosa and is widely believed to be the best test to detect colorectal cancer. In addition, colonoscopy allows for the detection and removal of colorectal adenomas -a well recognized colorectal cancer precursor. There is indirect evidence that suggests colonoscopy is effective in reducing colorectal cancer mortality, but to date, no large clinical trials have been completed to support this assumption. While colonoscopy use is increasing, data is emerging that colonoscopy may not be as effective as previously believed. Prior support for colonoscopy as a screening test relied upon effectiveness estimates that now appear to be overly optimistic. Given the invasive nature of colonoscopy, the associated small, but real risk of complications, and dramatically higher costs than other screening tests, it is especially important to determine the true comparative effectiveness of colonoscopy relative to other proven non-invasive options.
The investigators propose to perform a, large, simple, multicenter, randomized, parallel group trial directly comparing screening colonoscopy with annual FIT screening in average risk individuals. The hypothesis is that colonoscopy will be superior to FIT in the prevention of colorectal cancer mortality measured over 10 years. Individuals will be enrolled if they are currently eligible for CRC screening (e.g. no colonoscopy in the past 10 years and no FOBT in the past 1 year) and are between 50 and 75 years of age. The investigators will exclude individuals for whom colonoscopy is indicated (e.g. signs or symptoms of CRC, first degree family member with CRC, personal history of colorectal neoplasia or inflammatory bowel disease).
All participants will complete baseline demographic, medication, and lifestyle questionnaires (e.g. diet, non-steroidal anti-inflammatory use, frequency of exercise) prior to randomization in a 1:1 ratio to either screening colonoscopy or annual FIT screening (Figure 1). Those testing positive by FIT will undergo evaluation to determine appropriateness for colonoscopy. Screening will be performed in a manner consistent with the currently accepted standard of care in order to determine the comparative effectiveness of the two screening strategies. Participants will be surveyed annually to determine if they have undergone colonoscopy or been diagnosed with CRC.
The primary study endpoint will be CRC mortality within 10 years of enrollment. The secondary endpoints are (1) the incidence of CRC within 10 years of enrollment and (2) major complications of colonoscopy. Mortality will be determined through queries of the VA Vital Status File. Cause of death will be determined primarily using death certificates from the National Death Index-Plus database, augmented by adjudication of medical records for known CRC cases where CRC is not listed as a cause of death on the death certificate. The investigators postulate that screening colonoscopy will result in a 40% reduction in CRC mortality over 10 years relative to annual FIT screening. Using a log-rank test with a 2-sided test of significance, =0.05, a sample size of 50,000 participants will be required to test the primary hypothesis with 82% power, assuming a 1% annual rate of crossover from FIT to colonoscopy and a 0.5% annual rate of loss to follow-up. The planned study duration is 12.5 years with 2.5 years of recruitment and 10 years of follow-up for all enrolled participants.
