BACKGROUND: This report was produced for the Canadian Task Force on Preventive Health Care (CTFPHC) to provide guidelines on the screening of adults for colorectal cancer (CRC). The last CTFPHC guideline on this topic was published in 2001.
PURPOSE: To synthesize evidence on the benefits and harms of screening and the test properties of effective screening methods for asymptomatic adults who are not at high risk for colorectal cancer.
DATA SOURCES: The key question search was conducted in Medline, Embase and the Cochrane Library from January 2000 to November 2013.
STUDY SELECTION: The titles and abstracts of papers considered for the key question and subquestions were reviewed in duplicate; any article marked for inclusion by either team member went on to full text screening. Full text review was done independently by two people with consensus required for inclusion or exclusion. All studies reporting adverse effects of screening or follow-up tests as a result of screening were included, regardless of design.
DATA ABSTRACTION: Review team members extracted data about the population, study design, intervention, analysis and results for outcomes of interest. One team member completed full abstraction, followed by a second team member who verified all extracted data and ratings. We assessed study quality using Cochrane’s Risk of Bias tool and the GRADE framework. For the contextual questions, inclusion screening and abstraction were done by one person.
ANALYSIS: Relative risks (RRs), and 95% confidence intervals (CIs) were calculated using random-effects models. Test properties were reported using mean or median and ranges.
RESULTS: Meta-analysis of results of four moderate quality RCTs of screening with Guaiac Fecal Occult Blood Test (gFOBT) on CRC-specific mortality found a RR 0.82 (95%CI, 0.73, 0.92, I 2=67%), with an Absolute Risk Reduction (ARR) 2,654/million (1,128-4,010 fewer). Screening with gFOBT did not reduce all-cause mortality RR 1.00 (95% CI, 1.00-1.00, I2=0%). For late stage CRC, screening with gFOBT reduced late stage CRC by 8% RR 0.92 (95%CI, 0.85-0.99, I2=0%). One moderate quality RCT found that screening with Immunochemical Fecal Occult Blood Test (iFOBT) had a non-significant impact on CRC mortality RR 0.88 (95%CI, 0.72, 1.07). This was a one-time screen conducted in China. There were no data for iFOBT on all-cause mortality or incidence of late stage cancer. The meta-analysis of primary screening with flexible sigmoidoscopy showed a relative reduction of 28% in CRC specific mortality with a pooled RR of 0.72 (95% CI; 0.65, 0.81, I2=0%) and an ARR of 1,176 per million (95% CI; 830 to 1,486 fewer) in CRC specific mortality; RR 0.99 (0.97, 1.01, I2=35%) for all-cause mortality and RR 0.75 (95%CI, 0.66- 0.86, I2=23%); ARR 1,733/million (1,011, 2,368 fewer) for incidence of late stage cancer. Adverse events associated with FS are minor and major bleeding, infection and in rare cases death. The overall median sensitivity (55% were for a single screen) for iFOBT was of 81.5% (range 5.3-100%) and a median specificity of 95.0% (range 87.2%-96.9%) with a median PPV 7.35% (range 4.0%-10.8%), a mean NPV 100% (range 99.7%-100%) and NNS 209 (range 41-430). The overall median sensitivity of gFOBT was 47.1% (range 12.9%-75.0%) and a median specificity iii of 96.1% (90.1%-98.1%) with a PPV of 7.5 (1.5%-15%), a mean NPV of 99.55% (range 99.5%-99.6%) and the mean NNS 597 (range 239-936).
LIMITATIONS: There are no studies of effectiveness of colonoscopy, CT colonography or DNA tests on mortality or incidence of late stage CRC. The single iFOBT trial had only 8 year followup. The evidence used in this review could not answer several questions of interest including the optimal ages to begin and end screening, the optimal screening intervals, or if clinical benefits of screening differ for the various screening tests, or by subgroups.
CONCLUSION: Screening for CRC with fecal occult blood testing or flexible sigmoidoscopy are effective screening tools for colorectal cancer. However no conclusions can be drawn regarding the relative effectiveness of colonoscopy as a screening tool, or new tools such as CT colonography or DNA screening on overall mortality or incidence of late stage CRC. Although there is a lack of data on the impact of iFOBT on mortality the test prperties indicate that it is both sensitive and specific. It has been suggested that screening could be increased through better education about home-based fecal tests.