Methods: The purpose of this study was to assess the effect of screening for colorectal cancer on life expectancy and estimate the number of colonoscopies needed per life year saved. The declining exponential approximation of life expectancy was used to calculate the effect of colorectal cancer screening on expected remaining lifetime. The annual number of deaths from colorectal cancer and the size of the population were obtained from the vital statistics of the United States. Published reports were consulted to determine the decrease in mortality from colorectal cancer achieved by fecal occult blood testing, screening sigmoidoscopy or colonoscopy. A Markov chain analysis was used to determine the endoscopic resources required to screen and survey the entire population of U.S. residents age 50 years until death or age 85 years.
Results: Colorectal cancer decreases the life expectancy of U.S. residents aged 50 to 54 years by 292 days and those aged 70 to 74 years by 70 days. Screening with fecal occult blood tests extends expected lifetime of the 2 age groups by 51 and 12 days, respectively, whereas screening with sigmoidoscopy leads to increases of 86 and 21 days. Colonoscopic screening increases expected lifetime by 170 and 41 days, respectively. The number of colonoscopies needed to save 1 year of expected life ranges from 2.9 to 6.0, depending on the type of screening regimen used.
Conclusions: The extension of life through screening colonoscopy is two or three times longer than the extension achieved through flexible sigmoidoscopy or fecal occult blood test, respectively. Although a large number of colonoscopies are required to screen the U.S. population, relatively few colonoscopies need to be invested per year of life expectancy saved.