An efficient strategy for evaluating new non-invasive screening tests for colorectal cancer: the guiding principles

OBJECTIVE

New screening tests for colorectal cancer (CRC) are rapidly emerging. Conducting trials with mortality reduction as the end point supporting their adoption is challenging. We re-examined the principles underlying evaluation of new non-invasive tests in view of technological developments and identification of new biomarkers.

DESIGN

A formal consensus approach involving a multidisciplinary expert panel revised eight previously established principles.

RESULTS

Twelve newly stated principles emerged. Effectiveness of a new test can be evaluated by comparison with a proven comparator non-invasive test. The faecal immunochemical test is now considered the appropriate comparator, while colonoscopy remains the diagnostic standard. For a new test to be able to meet differing screening goals and regulatory requirements, flexibility to adjust its positivity threshold is desirable. A rigorous and efficient four-phased approach is proposed, commencing with small studies assessing the test's ability to discriminate between CRC and non-cancer states (phase I), followed by prospective estimation of accuracy across the continuum of neoplastic lesions in neoplasia-enriched populations (phase II). If these show promise, a provisional test positivity threshold is set before evaluation in typical screening populations. Phase III prospective studies determine single round intention-to-screen programme outcomes and confirm the test positivity threshold. Phase IV studies involve evaluation over repeated screening rounds with monitoring for missed lesions. Phases III and IV findings will provide the real-world data required to model test impact on CRC mortality and incidence.

CONCLUSION

New non-invasive tests can be efficiently evaluated by a rigorous phased comparative approach, generating data from unbiased populations that inform predictions of their health impact.

"Rescue" of Nonparticipants in Colorectal Cancer Screening: A Randomized Controlled Trial of Three Noninvasive Test Options

Few studies have directly targeted nonparticipants in colorectal cancer screening to identify effective engagement strategies. We undertook a randomized controlled trial that targeted nonparticipants in a previous trial of average-risk subjects which compared participation rates for mailed invitations offering a fecal test, a blood test or a choice of either. Nonparticipants (n = 899) were randomized to be offered a kit containing a fecal immunochemical test (FIT), directions on how to arrange a blood DNA test, or the option of doing either. Screening participation was assessed 12 weeks after the offer. To assess the cognitive and attitudinal variables related to participation and invitee choice, invitees were surveyed after 12 weeks, and associations were investigated using multinomial logistic regression. Participation rates were similar between groups (P = 0.88): 12.0% for FIT (35/292), 13.3% for the blood test (39/293), and 13.4% for choice (39/290). Within the choice group, participation was significantly higher with FIT (9.7%, 28/290) compared with the blood test (3.8%, 11/290, P = 0.005). The only variable significantly associated with participation was socioeconomic status when offered FIT, and age when offered choice but there was none when offered the blood test. Survey respondents indicated that convenience, time-saving, comfort, and familiarity were major influences on participation. There was no clear advantage between a fecal test, blood test, or choice of test although, when given a choice, the fecal test was preferred. Differences in variables associated with participation according to invitation strategy warrant consideration when deciding upon an invitation strategy for screening nonparticipants. PREVENTION RELEVANCE: This trial of screening for those at average risk for colorectal cancer targeted past fecal-test nonparticipants and compared participation rates for mailed invitations offering a fecal test, blood test, or choice of either. Although there was no clear advantage between strategies, factors associated with participation differed between each strategy.

Involvement of T helper type 17 and regulatory T cell activity in Citrobacter rodentium invasion and inflammatory damage

Citrobacter rodentium is a murine pathogen that transiently colonizes the lumen of the large intestine. C. rodentium induces colitis, but the relative importance and temporal induction of the T helper type 17 (Th17) and regulatory T cell (T(reg)) pathways in protection from the infection and inflammation have not been assessed. Our aim was to investigate the key immunological signalling events associated with successful clearance of C. rodentium. Mice were challenged with luminescent-tagged C. rodentium and killed at days 3 (early infection), 10 (peak infection) and 21 (late infection) post-infection. Bioluminescent imaging and bacterial culture determined levels of C. rodentium. Distal colon mRNA expression of interleukin (IL)-17, IL-6, IL-1beta, tumour necrosis factor (TNF)-alpha, forkhead box P3 (FoxP3) and ghrelin were assessed using real-time polymerase chain reaction. Results were compared with age-matched non-infected mice. Low levels of C. rodentium were found at day 3, high levels at day 10, with clearance from the majority of the mice by day 21. In the distal colon, there was up-regulation of TNF-alpha and FoxP3 throughout the study and increases in IL-6 and IL-17 during the peak and late stages of infection. Ghrelin expression was increased at the peak and late stages of infection. This study has characterized changes to the T helper cell pathways, following the course of C. rodentium infection in mice. There were significant immunological changes, with up-regulation of the Th17 and T(reg) pathways in the distal colon and an increase in ghrelin expression compared with non-infected control mice. These changes may play a role in the pathology and clearance of C. rodentium.

Assessment of gastric emptying in the mouse using the [13C]-octanoic acid breath test

1. Gastric emptying studies in small laboratory animals are hampered by the deficiency of a technique that is non-invasive and repeatable. The aim of the present study was to adapt the non-invasive [13C]-octanoic acid breath test, which has been validated in humans, to assess both liquid and solid gastric emptying in the mouse. 2. Gastric emptying rates were investigated for a liquid meal (Intralipid; Kabi Pharmacia AB, Stockholm, Sweden; n = 7) and two solid meals (egg yolk and mouse chow; n = 7) incorporating [13C]-octanoic acid. All meals were analysed for natural enrichment of [13C]. Mathematical analysis of the 13CO2 excretion rate allowed the determination of gastric emptying parameters. 3. Gastric emptying of Intralipid was more rapid than egg yolk (P < 0.0001). Gastric emptying of mouse chow could not be assessed due to intragastric separation of [13C]-octanoic acid and natural [13C] enrichment of the pellet. 4. The [13C]-octanoic acid breath test can reproducibly assess both liquid and solid gastric emptying non-invasively in the mouse. This method can now be used to assess gastric emptying in drug studies and disease studies for which there are established mouse models.