The impact of screening on colorectal cancer mortality and incidence: has it really made a difference?

Abstract

About sixty percent of the US population of those age fifty and older are currently up to date with colorectal cancer screening recommendations. Has this level of screening made a difference for reducing colorectal cancer (CRC) incidence and/or mortality? Randomized controlled trials of guaiac-based fecal occult blood tests, which have relatively low sensitivity but high specificity for CRC, have shown a modest effect but with a long-term reduction in CRC mortality. Newer fecal immunochemical tests are expected to have a greater effect. Randomized controlled trials of flexible sigmoidoscopy have also demonstrated a reduction in CRC mortality. Observational studies of screening colonoscopy suggest an effect of greater than fifty percent reduction in CRC mortality. We have assessed past trends of colorectal cancer screening in the US population which suggest that more than fifty percent of the decline in colorectal cancer mortality can be attributed to the increased acceptance and uptake in colorectal cancer screening. Current and future levels of increased screening could provide for even larger reductions for the USA. Colorectal cancer screening has and will continue to make a significant impact on reducing colorectal cancer mortality.

Figure 1. Age adjusted rates from 1975 to 2011 for CRC Incidence and Mortality [1]

Red line is for CRC incidence and black line for CRC mortality. Source data from ref .

Figure 2. CRC Mortality in the National Polyp Study for Adenoma and Non-adenoma patients with comparison with the US incidence based mortality rates over up to 20 years

The number of subjects at risk per years followed is given for the adenoma (blue line) and non-adenoma (red line) cohorts. The cumulative incidence based mortality for the average risk US Population is taken from SEER data (black line). There were 25 CRC deaths expected in the general population of comparable age and sex distribution as the NPS adenoma cohort. There were 12 observed deaths in the NPS cohort with adenomas removed for a 53% reduction in CRC mortality compared to general population rates. Reproduced with permission from ref .

Figure 3. Partition of Past Trends in Colorectal Cancer Incidence and Mortality (1975–2000)

Microsimulation model estimates of the contribution of risk factors and screening on CRC incidence (3a) and these factors as well as treatment on CRC mortality (3b). The black line is the observed SEER (9) delay-adjusted colorectal cancer incidence rates based on first primary colorectal cancer (Figure 3a) and the age-adjusted CRC mortality rates (Figure 3b) for 1975–2000. The green shaded area represents the estimate of the contribution of risk factor modification and the orange shaded area represents the estimate of the additional contribution of screening to the decline in CRC incidence (3a) and mortality (3b). The purple shaded area in 3b represents the estimate of the additional contribution of treatment to the decline in CRC mortality. Reproduced with permission from refs ,.

Figure 3. Partition of Past Trends in Colorectal Cancer Incidence and Mortality (1975–2000)

Microsimulation model estimates of the contribution of risk factors and screening on CRC incidence (3a) and these factors as well as treatment on CRC mortality (3b). The black line is the observed SEER (9) delay-adjusted colorectal cancer incidence rates based on first primary colorectal cancer (Figure 3a) and the age-adjusted CRC mortality rates (Figure 3b) for 1975–2000. The green shaded area represents the estimate of the contribution of risk factor modification and the orange shaded area represents the estimate of the additional contribution of screening to the decline in CRC incidence (3a) and mortality (3b). The purple shaded area in 3b represents the estimate of the additional contribution of treatment to the decline in CRC mortality. Reproduced with permission from refs ,.

Figure 4. Projections of Colorectal Cancer Mortality

Microsimulation model projecting the effect of three levels of cancer control interventions on risk factors, screening, and treatment on CRC mortality (4a) and the estimated contribution of risk factors, screening and treatment to the optimistic projections for CRC mortality (4b). The black line is the age adjusted US mortality rate (1975–2006) by year of death. The gray line is the MISCAN modeling of the age-adjusted mortality 1975 to 2000 based on the past trends in risk factors, screening, and treatment (the purple line of Figure 3). In 4a, the blue line represents the projected CRC mortality if the upstream factors for risk factors, screening, and treatment remain at the same level as for 2000. This scenario is called Frozen (at 2000). The orange line represents the projected CRC mortality if the upstream factors continued according to the trend of these factors in 1995–2000. This scenario is called Continuing Trends. The red line represents the projected CRC mortality if the upstream factors for risk factors, screening, and treatment improve over and above that of continued trends to an optimistic level for each factor. This scenario is called optimistic trends. The blue area represents the improvement in CRC mortality based on the pre-2000 trends in upstream factors. The yellow area represents the additional impact of post-2000 continued trends in upstream factors. The red area represents the additional impact of post-2000 optimistic trends in upstream factors. In 4b, the heavy blue line is the MISCAN model projection based on pre-2000 upstream factors (Frozen scenario) (blue line of 4a). The next lines represent the individual components of the Opportunistic Trends models. The green line represents the projected age-adjusted CRC mortality if only optimistic treatment interventions are implemented. The orange line represents the age adjusted CRC mortality rate if only optimistic risk factor interventions were implemented. The purple line represents the CRC mortality rate if only optimistic screening were implemented. The heavy red line represents the CRC mortality rate for the combined effect of implementing risk factor, screening, and treatment interventions. Reproduced with permission from refs ,.

Figure 4. Projections of Colorectal Cancer Mortality

Microsimulation model projecting the effect of three levels of cancer control interventions on risk factors, screening, and treatment on CRC mortality (4a) and the estimated contribution of risk factors, screening and treatment to the optimistic projections for CRC mortality (4b). The black line is the age adjusted US mortality rate (1975–2006) by year of death. The gray line is the MISCAN modeling of the age-adjusted mortality 1975 to 2000 based on the past trends in risk factors, screening, and treatment (the purple line of Figure 3). In 4a, the blue line represents the projected CRC mortality if the upstream factors for risk factors, screening, and treatment remain at the same level as for 2000. This scenario is called Frozen (at 2000). The orange line represents the projected CRC mortality if the upstream factors continued according to the trend of these factors in 1995–2000. This scenario is called Continuing Trends. The red line represents the projected CRC mortality if the upstream factors for risk factors, screening, and treatment improve over and above that of continued trends to an optimistic level for each factor. This scenario is called optimistic trends. The blue area represents the improvement in CRC mortality based on the pre-2000 trends in upstream factors. The yellow area represents the additional impact of post-2000 continued trends in upstream factors. The red area represents the additional impact of post-2000 optimistic trends in upstream factors. In 4b, the heavy blue line is the MISCAN model projection based on pre-2000 upstream factors (Frozen scenario) (blue line of 4a). The next lines represent the individual components of the Opportunistic Trends models. The green line represents the projected age-adjusted CRC mortality if only optimistic treatment interventions are implemented. The orange line represents the age adjusted CRC mortality rate if only optimistic risk factor interventions were implemented. The purple line represents the CRC mortality rate if only optimistic screening were implemented. The heavy red line represents the CRC mortality rate for the combined effect of implementing risk factor, screening, and treatment interventions. Reproduced with permission from refs ,.