Researchers used microsimulation modeling to analyze the historical impact of changes in risk factors, screening and treatment practices, and to project future mortality trends for colorectal cancer. The model, named MISCAN-Colon, which was developed by NCI's Cancer Intervention and Surveillance Modeling Network (CISNET) consortium, simulates the U.S. population from 1975 through 2020. The model includes factors that could increase risk for colorectal cancer (i.e., smoking, obesity, and red meat consumption), as well as factors that could decrease colorectal cancer risk (i.e., aspirin use, consumption of supplements such as folate and calcium, and physical activity). To calculate screening use, researchers used national data on the use of fecal occult blood testing (which looks for blood in stool samples), and endoscopy (including flexible sigmoidoscopy and colonoscopy, which allows doctors to examine the lower part of the colon or the entire large intestine, respectively). To assess the effects of treatment, researchers assessed data on use of, and disease-free survival rates associated with, four chemotherapy regimens used for advanced colorectal cancer during different historical time periods.
Using the model, the researchers were able to estimate the impact of historical changes in risk factors, screening practices, and treatment advances on past changes in incidence and mortality, as well as predict future trends through 2020.
From 1975 to 2000, colorectal cancer incidence fell 22 percent, half of which was most likely due to changes in risk factors, and half due to screening. Similarly, colorectal cancer deaths fell by 26 percent during that time period, with a 9 percent drop resulting from a change in risk factors, a 14 percent drop from screening, and a 3 percent drop from improved treatment.
The researchers created projections to look at how colorectal cancer mortality trends could change with varying levels of cancer control interventions. If there were no changes in risk factors, screening or treatment (stable since 2000), Americans could expect a 17 percent decline in colorectal cancer mortality from 2000 to 2020. However, if current trends persist, Americans could see a 36 percent decline in colorectal cancer mortality. With accelerated cancer control efforts, there could be an overall colorectal cancer mortality reduction of 50 percent by 2020.
"The extraordinary progress on colorectal cancer shows what can be achieved by coordinated and targeted efforts to apply existing knowledge to cancer control at the state and federal level," said John R. Seffrin, Ph.D., chief executive officer of the American Cancer Society. "Increases in colorectal cancer screening have been achieved through a variety of efforts, including education of the public and medical community and advocacy for health insurance coverage of the full range of colorectal cancer screening tests. The American Cancer Society is committed to continuing these efforts to get as close as we can to the potential 50 percent colorectal cancer mortality reduction that this report says is possible."