Estimating the magnitude of colorectal cancers prevented during the era of screening: 1976 to 2009.

BACKGROUND: Ideally, screening detects cancer at a more curable stage and, as a result, decreases the rate of subsequent diagnosis at a late stage. Although it is suggested that some cancer screening tests have led to substantial increases in early-stage incidence with only marginal reductions in late-stage incidence (eg mammography), the association between temporal trends in colorectal cancer screening and its cumulative impact on colorectal cancer incidence is unknown.
METHODS: Colorectal cancer incidence data spanning over 3 decades (1976-2009) were collected from the Surveillance, Epidemiology, and End Results database. Data on screening use spanning the period from 1986 to 2010 were collected from the National Cancer Institute Cancer Trends Progress Report, and trends in the incidence of early-stage (in situ, local) and late-stage (regional, distant) colorectal cancer were examined among adults aged ≥50 years.
RESULTS: From 1987 to 2010--the years for which screening data were available--the percentage of adults aged ≥50 years who underwent screening rose from 34.8% to 66.1% (which included increases in colonoscopy). During that time, the incidence of late-stage colorectal cancer decreased from 118 to 74 cases per 100,000 population (P < .001). The incidence of early-stage colorectal cancer also decreased, from 77 to 67 cases per 100,000 population (P < .001). After adjusting for underlying trends in cancer incidence, colorectal screening was associated with a reduction of approximately 550,000 cases of colorectal cancer over the past 3 decades in the United States.
CONCLUSIONS: There has been a significant decline in the incidence of colorectal cancer in the United States, particularly for late-stage disease, during a time of increasing rates of screening.