New research from Sweden offers a nuanced look at colorectal cancer screening methods, comparing the effectiveness of a one-time colonoscopy to two rounds of fecal immunochemical testing (FIT). The large-scale study, known as SCREESCO, involved over 278,000 individuals and provides valuable data on both the benefits and potential harms of different screening approaches.
Understanding the Study Design
The SCREESCO trial, conducted between and , randomly assigned participants to one of three groups: a one-time colonoscopy, two rounds of FIT screening two years apart, or a control group receiving usual care. The study aimed to assess the impact of these interventions on colorectal cancer (CRC) mortality and incidence. Participants were aged 60 or turning 60 during the study period and were drawn from 18 of Sweden’s 21 regions. Individuals with a prior CRC diagnosis or participation in another related trial were excluded.
The study’s design included a later phase where an additional 77,280 individuals were randomized to either colonoscopy or the control group, addressing lower-than-expected participation in the initial colonoscopy arm. This resulted in a total of 31,113 individuals in the colonoscopy arm, 60,267 in the FIT arm, and 186,671 in the control group.
Key Findings: Detection Rates and Stage
After a median follow-up of 4.8 years, researchers found that both colonoscopy and FIT screening increased CRC detection compared to usual care. However, the increase was more pronounced for earlier-stage cancers. The incidence rate of CRC was 107.9 per 100,000 person-years in the colonoscopy arm and 99.9 in the control group (incidence rate ratio or IRR of 1.08, 95% confidence interval 0.91-1.28). For the FIT arm, the incidence rate was 96.0 per 100,000 person-years compared to 103.9 in controls (IRR of 0.92, 95% CI 0.81-1.05).
Importantly, rates of stage I–II CRC were higher in both the colonoscopy arm (IRR: 1.38, 95% CI: 1.09–1.74) and the FIT arm (IRR: 1.19, 95% CI: 0.99–1.43) compared to controls. This suggests that both screening methods are effective at detecting cancers at an earlier, more treatable stage.
Adverse Events and Usual Care in Sweden
The study also examined potential harms associated with screening. Researchers observed slightly higher rates of cardiovascular and gastrointestinal events in the intervention arms during the first year, which then became more similar to the control group. These events included gastrointestinal bleeding, splenic injury, and cardiovascular events like ischemic heart disease. The study carefully monitored serious adverse events reported by endoscopy units.
It’s important to note the context of “usual care” in Sweden. Unlike some countries with national screening programs, Sweden relies primarily on symptom-driven diagnoses. While FIT is increasingly used as an initial step in investigating symptoms, there was no nationwide organized screening program during the study period. Individuals may also undergo colonoscopy due to surveillance for increased CRC risk, such as those with a history of inflammatory bowel disease or familial CRC syndromes.
Study Limitations and Future Research
The researchers acknowledge several important considerations. Masking was not possible due to the nature of the trial, meaning participants were aware of which group they were assigned to. The study’s primary endpoint – CRC mortality – will not be known until , requiring longer-term follow-up. The initial power calculations were based on assumptions about participation rates, which were adjusted during the study as enrollment varied.
The study protocol underwent revisions, including adjustments to power calculations and the timing of analyses. These changes were made in response to observed participation rates and to ensure the study’s ability to detect meaningful differences. The researchers emphasize that the current analysis focuses on the diagnostic phase of the trial and does not represent an interim analysis of CRC mortality.
Implications for Colorectal Cancer Screening
The SCREESCO trial provides valuable evidence supporting the benefits of both colonoscopy and FIT screening for colorectal cancer. The finding that both methods increase the detection of early-stage cancers is encouraging. However, the observed increase in adverse events, even if temporary, highlights the importance of carefully considering the risks and benefits of screening. Further research, particularly long-term follow-up to assess CRC mortality, is needed to refine screening strategies and optimize patient outcomes. The study is registered with ClinicalTrials.gov under number NCT02078804.
