Review for 10.1186/s12876-022-02331-9 (2022)

Title: Colorectal Cancer Screening Participation among Citizens not recommended to be
screened: A Cohort Study
Version: 1 Date: 18 Feb 2022
Reviewer's report:
The manuscript describes the uptake rates as well as positivity rates among the groups of people
which are recommended not to participate. It is a relatively simple but useful study for all
colorectal cancer screening managers and policy makers. It provides information not easy to
retrieve in many areas, where the information on previous diseases at a population level is not
available or not updated.
Overall the manuscript is easy to follow and the tables and conclusions quite straightforward.
I have several comments though regarding the screening context, methods, and interpretation
of the results:
1. Abstract- Background: “whom not to invite” is equivalent to “exclusions”, which is the
standard nomenclature in many screening programs. I wonder why authors do not use these
concepts (here as well as in the rest of the manuscript)
2. Abstract-Materials: “Screening participation rates and false-positive rates were calculated”
but afterwards there is no mention of FP rates, only positivity rates, which were not mentioned
in the abstract
3. “Residents” – it is not common as far as I know to use this concept in articles of screening,
but rather “invitees”, invited population, etc
4. Abstract – results: I suggest to improve the paragraph, using a simpler way to provide
the results. Also I believe there is a mistake “and SIGNIFICANTLY/NON-SIGNIFICANTLY
higher among the high-risk groups”
5. Background: it would be useful to explicitly describe what does the invitation say about
the groups of the study (CRC, previous adenoma, surveillance, IDB, etc). “the invitation letter
states that these residents should not participate. Furthermore, the invitation letter encourages
individuals with IBD to discuss whether participation”. The wording of this letter is important
to better interpret the results and extrapolate them to other programs.
6. Setting:
a. what does “first round” mean in Denmark? March 2014 to December 2017 is almost 4 years,
and rounds are usually the same length as the screening interval (2 years)
b. “Residents who turned 50 or 75 years during the first screening round were invited just before
their birthday” – what about those who turned 51, 52, 53, etc? when were they invited?
c. FIT units – please review. Usually they are described in micro-grams per g of feces (check
also line 140)
7. line 104: The analysis is not whether or not, but to what extent high risk residents participate,
the participation rate in each group
8. line 109: why this study period? It should be justified here, not (or not only) in the discussion
9. line 118-119: 3 groups: Why 10 years for group 3, if the group 1 is partially defined with a
20 year interval of polyp diagnose? The definition of the groups and subcategories is partially
confusing. Could there be risk of overlapping categories or non-mutually exclusive categories?
10. line 125: Crohn’s DISEASE
11. line 175-176: please specify if this is a Danish legal document
12. line 179: this sentence may be valid in Denmark, but not everywhere. Thus, better add ”As
this is... study, in Denmark ...is not required”
Results
13. ” 14,202 (2.3%) were excluded due to a colorectal adenoma diagnosis within the last 10 years
as the only known colorectal disease” – I am not sure I understand why they were excluded.
Wouldn’t these fall into the ” high CRC risk highly likely to be enrolled in a surveillance
programme” category?
14. line 200: Since this is a description of the main results, please specify the exact figures of
participation (not ”approximately two thirds” etc)
15. Table 3: the ORs are not at all interpreted nor even mentioned in the text. Either remove
them from the table (with 95%CI might be sufficient) or add the unadjusted OR as well as the
adjusted and provide an interpretation, in order to understand the effect of sex and age.
Discussion
16. It is important to interpret the results in line with what exactly says on the letter that invitees
receive.
17. line 249. What do authors mean with ”appears to high”? Does that mean that authors question
the truthfulness of the records, risk of miss-classification bias or simply surprise of how little
these people comply with recommendations on the letter...? please provide more information as
this is the central point of the study
18. line 254 ” As we only had information on participation until July 2016” -- How so? The
justification of the study period should be included in the methods section
19. Line 276 ” it constitutes a resource pull for both society and residents” – I am not sure what
this means. Do authors mean unnecessary burden to the healthcare system? I would argue that
this can only be stated if we can assure that these people are also on the proper surveillance
protocols.
Another relevant point to reflect on is why they choose to participate, and what are healthcare
services providers and managers ”doing wrong” in terms of communication or else that they feel
compelled to participate? Why do they believe that participating is the best option for them?
Also, could the performance of a simple non invasive test at home prevent people from adherence
to their next visit and/or colonoscopy, feeling it is not longer necessary? And thus participating
in the program do ”more harm than good”...? These are all issues that would be necessary to
be reflected on.
20. In the Discussion, there is no comparison with other studies or findings around the same
topic. If authors could not find any similar studies, they should state this. But also, find for
studies on the same topic but perhaps other cancer screening or healthcare preventive services.
21. As part of the conclusions, authors should also mention the higher positivity rate in the higher
risk groups, except CRC
Tables
All tables should be self-explanatory; i.e. all acronyms should be defined again either in the title
or the foot of the table.
Table 2. If you provide proportion of women, the proportion of men is not needed.
Table 3 and 4: consider either removing the adjusted OR, or adding the unadajusted OR, and if
so, adding the interpretation to the text
Table 4: There are several errors here, as it should be participants with a valid tests (not Invited)
and positive results (not participants). Also, what does is mean ”<5” for IBD with PSC?