Study design
The mtFIT study is a cross-sectional intervention study with a paired design comparing mtFIT to FIT. Participants will take two samples from the same bowel movement. One of the laboratories appointed to analyze FIT samples collected during the Dutch national CRC screening program will also analyze the mtFIT samples. If either or both tests are positive, participants are referred for colonoscopy. All colonoscopy and pathology data are collected and centrally stored in a national screening database (ScreenIT; Topicus, Deventer, The Netherlands), managed by the screening organization, and will be retrieved for this study. As recommended by the Dutch Health Council, the ethical review and approval of the study were issued by the Dutch Ministry of Health, Welfare and Sport in April 2020. The study is registered in ClinicalTrials.gov (NCT05314309) [25]. The current mtFIT study is being conducted with the FAIR principles in mind: to have the data be Findable, Accessible, Interoperable and Reusable.
Study population
The mtFIT study is conducted in an intended-use population [18, 26]. To this end, participants are randomly selected from the target population of the Dutch national CRC screening program (n = 2.000.000 annually). The screening organization will send invitations until 13,131 participants are included. Inclusion criteria for the mtFIT study are equal to those of the Dutch national CRC screening program. Dutch residents aged 55 to 75 years old are eligible, except for those [1] undergoing treatment for CRC, or [2] having had a colonoscopy less than 5 years ago, or [3] undergoing colonoscopy surveillance because of another gastrointestinal disease or [4] because of an increased risk of CRC due to a hereditary or familial CRC syndrome. In order for subjects to be able to read the participant information and give informed consent, they need to have a sufficient understanding of the Dutch language.
Sample size calculation
The sample size is based on the McNemar test for testing the difference in detection rates between mtFIT and FIT in a paired design. The calculation used data reported by the screening organization for 2020, with a FIT detection rate for AN of 1.2%, and assumed that mtFIT would result in a 20% increased detection rate of 1.44%. Then, under the assumption of an 80% overlap in AN detection, a two-sided significance level of 5%, and a power of 90% to detect a 20% increased detection rate, a total number of 13,131 participants is required.
Subject recruitment and informed consent
The screening organization, responsible for executing the Dutch national CRC screening program, selects and recruits subjects. A computer-run algorithm selects a random sample from the participants of the Dutch national CRC screening program (SPSS, version 23, IBM Corp, Armonk, NY). Each subject has an unique study code used in all correspondence. An invitation is sent to subjects four weeks prior to their planned regular screening invitation, informing them about the study and giving them the opportunity to participate. This invitation includes an information brochure, an informed consent form, and a link to the study website which contains an animation video explaining the study, and all study brochures (in Dutch) [27]. Individuals participating in the study have to sign the informed consent form and send it to the Netherlands Cancer Institute, where the informed consent is stored following the European General Data Protection Regulation. In addition to requesting informed consent for participation in the study, participants are also asked for permission to re-use obtained data and material for future research into early detection of CRC, including the storage of collected stool samples in a biobank and keeping residual material obtained during a possible colonoscopy.
Sample collection
Approximately four to eight weeks after their study invitation, at the moment of their planned invitation for the Dutch national CRC screening program, participants receive a participation package. This package includes an information brochure on the national CRC screening program and the mtFIT study, instructions for collecting the stool samples for the two tests, two collection tubes, a plastic sealing bag for safely shipping the collection tubes, and a return envelope (Fig. 1, step 1). The FOB-Gold (Sentinel, Milan, Italy) collection tube is used for FIT and the OC-Sensor (Eiken Chemica Co., Tokyo, Japan) for mtFIT. After completing the stool collection, the samples are returned to the laboratory by postal mail. Except for the extra collection tube and associated information, the study package is similar to the package used in the Dutch national CRC screening program.
Laboratory procedures
The laboratory checks the returned envelopes for the presence of both FIT and mtFIT. When a participant returns just one of two collection tubes, he/she will be excluded from the study. If only the FIT is returned the FIT is analysed for the regular CRC screening program. In the laboratory, the two collection tubes follow separate workflows.
FIT samples will be analyzed according to the standard operating procedures of the Dutch national CRC screening program, using a fully-automated clinical chemistry analyzer (Bio Majesty JCA, DiaSys Diagnostic Systems, Holzheim, Germany). Quantitative hemoglobin test results for every sample are automatically communicated to the screening organization and stored in the ScreenIT database (Fig. 1, step 2). The used FIT cut-off for positivity is 47 μg hemoglobin / g feces and is similar to the cut-off used in the regular Dutch national CRC screening program [28].
For mtFIT, the assay, developed using the Meso Scale Discovery (MSD) platform, measures the hemoglobin, calprotectin, and serpin family F member 2 proteins with tailored antibody assays, using electrochemiluminescence [29]. The study setup allows for the analysis of 37 samples (in duplo) per run, next to multiple controls. For each protein, the mean of the duplicate values is computed and fed into the previously described mtFIT algorithm [12]. The mtFIT result is then communicated to the screening organization and stored in the ScreenIT database (Fig. 1, step 2).
Final test result
Within 10 days of the arrival of the sample at the laboratory, the screening organization informs the participant of the final positive or negative stool test result. The result is positive if FIT and/or mtFIT are positive and negative if both FIT and mtFIT are negative (Fig. 1, step 3). For positive results, both the participant and the endoscopist are blinded for which test(s) was (were) positive. If a participant wants to know which test(s) was (were) positive before the colonoscopy, the participant will be excluded from the study.
Clinical procedures
In the event of a positive stool test result, participants are referred for colonoscopy (Fig. 1, step 3). All lesions detected during colonoscopy are removed and sent for pathological evaluation. The quality of the colonoscopy and pathology examinations is controlled in the Dutch national CRC screening program, including certification of the centers and the individual endoscopists [30]. This includes structured reporting of both colonoscopy and pathology data in ScreenIT [31, 32]. The data of study participants will be made available to the study team in a pseudonymized form. AN is defined as the presence of a CRC, an advanced adenoma or an advanced serrated polyp. CRC stage is defined based on the American Joint Committee on Cancer TNM classification system. Advanced adenomas are defined as adenomas with a size ≥10 mm and/or high-grade dysplasia and/or a villous component (e.g. tubulovillous or villous adenoma). Advanced serrated polyps are serrated polyps with a size ≥10 mm and/or with any grade of dysplasia (Fig. 2).
Data collection, management and monitoring
To define data management processes and workflow, the research team has developed standard operating procedures that follow the Good Clinical Practice guidelines. Study data are compiled and stored in the web-based electronic data capture system ‘Castor EDC’ (Ciwit B.V., Amsterdam, the Netherlands). Informed consent and participants’ data are pseudonymized by the screening organization, using unique identification codes. Each sample tube, either mtFIT or FIT, has a unique code with which the laboratory reports the mtFIT results to the study team. Only the screening organization has access to information that may reveal a participants’ identity.
For data sharing and transfer of the various data types obtained during this study, a secure cloud storage called Surfdrive (SURF, Utrecht, the Netherlands) is used that complies with the Dutch and European privacy legislation [33]. Access to the cloud storage is restricted to study staff, including the researchers, screening organization and laboratory, and granted at folder level.
Data monitoring is performed regularly to check completeness of data entry and warnings from the validation rules. Incidents regarding data and study logistics are documented and reviewed with the screening organization and the National Institute of Public Health and the Environment.
The study team aims to ensure that end-of-study integrated data complies with the FAIR principles using the cBioPortal platform hosted for Dutch institutions through Health-RI [34].
Data analysis
Since colonoscopy data will only be available for participants with a positive FIT and/or mtFIT, absolute sensitivities of both tests cannot be determined. Therefore, the performance of mtFIT will be compared to FIT by determining the relative sensitivity (calculated as the relative detection rate) for AN as well as CRC, advanced adenomas and advanced serrated polyps, respectively. This comparison will be performed at an equal positivity rate.
Health economic modelling
The externally validated Adenoma and Serrated pathway to Colorectal Cancer (ASCCA) model will be used to assess the long-term cost-effectiveness of programmatic mtFIT- versus FIT-based screening [35]. We will first set up the model to simulate the current Dutch national CRC screening program, which consists of biennial FIT-based screening between the age of 55 and 75 years. Participation to FIT and colonoscopy will be set to 73 and 92%, respectively, following the observed participation rates in the Dutch national CRC screening program. Subsequently, we will set up the model to simulate mtFIT-based screening, assuming the same screening protocol and participation rates as for FIT-based screening. The sensitivities of FIT for separate lesion types (i.e., CRC, advanced adenomas, advanced serrated polyps, non-advanced adenomas, non-advanced serrated polyps) that are currently used in the ASCCA model will be adapted with the relative sensitivities of mtFIT compared to FIT at an equal positivity rate to obtain absolute sensitivities of mtFIT. Outcomes of each screening strategy will include the number of CRC cases and deaths, number of colonoscopies, quality adjusted life-years and costs. The mtFIT-based screening will be compared to FIT-based screening by calculating CRC incidence and CRC-related mortality reductions as well as the incremental cost-effectiveness ratio (ICER) (the difference in costs divided by the difference in quality adjusted life-years). In addition, a threshold analysis will be performed to determine the maximal costs of the mtFIT at which mtFIT-based screening will be cost-effective compared to FIT-based screening assuming a willingness-to-pay threshold of €45.874 corresponding to the Dutch gross domestic product per capita in 2020 [36, 37].