Who benefits from Colorectal Cancer Screening? A subgroup Analysis of the Minnes

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DESCRIPTION (provided by applicant): 1. To determine the effect of fecal occult blood testing (FOBT) screening on colorectal cancer mortality, non- colorectal cancer mortality and all-cause mortality in the Minnesota Colon Cancer Control Study, (MCCCS) updated to 2006 2. To determine the effect of FOBT screening on colorectal cancer mortality and non-colorectal cancer mortality by age (by 5 and 10 year age groups) and gender in the MCCCS updated to 2006 3. To determine the independent influence of baseline characteristics on colorectal cancer mortality and non-colorectal cancer mortality in the MCCCS. Significance: Most guidelines recommend starting screening for colorectal cancer at age 50 years for average risk individuals. The earliest and most tested strategy among these is FOBT, supported by four large randomized clinical trials that established the effectiveness of colorectal cancer screening. The Minnesota Colon Cancer Control Study was conducted in Minnesota, US. The trial recruited healthy volunteers between the ages of 50 to 80. The trials have not reported results stratified by age and gender. Additionally, the effects of other baseline variables, such as co-morbidities and intake of aspirin on outcomes have not been reported. A recent meta-analysis of these trials confirmed a reduction in colorectal cancer mortality (RR 0.87; 95% CI 0.8-0.95), but also reported an increase in non-colorectal cancer mortality of approximately equal absolute magnitude (RR 1.02; 95% CI 1.00-1.04) so that overall mortality was nearly identical (RR 1.002, 95% CI 0.989-1.015). Why non-CRC mortality would be increased is unclear, but one possibility is that the FOBT trials included some individuals that benefited from CRC screening, and other individuals who experienced net harm. Therefore, detailed sub-group analyses of the FOBT trial data, to separate out sub- groups that benefit from screening from those who may potentially be harmed would be important. For example, patients over age 70 or 75 might derive less benefit and more harm from screening, in which case screening this population may need to be re-considered. The goals of this research are to evaluate if effects of screening on colorectal cancer mortality seen 18 years after randomization (reported in 1999) in the Minnesota Colon Cancer Control Study persist, or are different 28-30 years after randomization (when updated to year 2006), and whether effect of screening for colorectal cancer varies in age and gender sub- groups. We also wish to evaluate the influence of baseline characteristics, such as diet, aspirin use and body mass index on these outcomes. Project Design and methods: This project involves updating the vital status and cause of death of all participants from the Minnesota Colon Cancer Control Study up to 2006 and calculating CRC, non-CRC and all-cause mortality estimates. We plan to compare colorectal cancer (CRC) mortality and non-colorectal cancer mortality rates between the screened and unscreened groups, by age categories at time of randomization of 5 year (50-54, 55-59, 60-64, 65-69, 70-74, 75-80) and 10 year (50-59, 60-69, 70-80) intervals. We will also stratify the above analyses by gender subgroups. No patient baseline data other than age and gender has been analyzed or reported from the Minnesota Colon Cancer Control Study. A 4-page, 56-item baseline questionnaire was completed by participants. We will perform a quality check on the existing data files to determine if re-entry is required for all or a subset of the questions on the baseline questionnaire. We are interested in exploring the relationship between consumption of NSAIDs, high fiber diet and BMI as effect modifiers of effectiveness of screening. PUBLIC HEALTH RELEVANCE: VA has put much effort into studying and implementing colorectal cancer screening. Colorectal cancer incidence increases with age. It is one of the most common cancers among the veteran population. Lieberman et al57 reported an incidence rate of 5.9% for colonic lesions among asymptomatic veterans undergoing screening colonoscopy. An estimated 75% of VA patients are over age 50, and 40% are over age 70. Also, women constitute 5% of veteran patients, and the number is expected is increase. A recent VA study has called attention to CRC screening in elderly veterans with serious co- morbidities who are unlikely to benefit 1. It is therefore important to clarify whether screening is beneficial in all sub-groups. A better understanding of the ideal target population to be screened would help focus efforts at resource-effective implementation.