Review for 10.1186/s12876-019-1052-7 (2019)

Reviewer’s report
Title:  Case Report of Synchronous Post-Lung Transplant Colon Cancers in the Era of Colorectal
Cancer Screening Recommendations in Cystic Fibrosis: Screening “Too Early” Before It’s Too Late?
Version: 0 Date: 21 Dec 2018
Reviewer: Iris Lansdorp-Vogelaar
Reviewer's report:
The authors describe a case report of a CF patient developing with synchronous CRC 3 years after a
prior normal colonoscopy. Their reporting of this case illustrates the importance of careful monitoring
of  CRC  in  CF  patients.  As  the  authors  rightfully  point  out,  much  is  still  unknown  about  the
development of CRC in CF patients, and this case could very well illustrate the importance of more
intensive surveillance of CF patients for adenomas and CRC. 
However, as for all population screening, the benefits of earlier surveillance should always be weighed
against its harms. Currently I find the conclusion of the case report too strong:
- In all population screening programs interval cancers occur. It is the frequency of these interval
cancers that should determine whether the interval for rescreening should be shortened. One
case is certainly not enough to warrant a shorter screening interval. It could be used as an alert
to ensure that interval cancers in this population should be monitored. 
- The large size of the CRC in the transverse colon seems to suggest a rapid progression of disease.
However, given the symptoms of the patient 3 years prior, it could also signify a missed cancer,
which is not unlikely. Again, this one case is insufficient to draw any conclusions in this respect.
- Although rare, synchronous cancers also occur in 5% of CRC cases in the general population. This
does not necessarily mean that the screening interval needs to be shortened. 
In summary, I feel this is an important case report to present, but the conclusion of this work should be
that further monitoring is needed to better elucidate whether this case is an exception or indeed an
indication for a need to revisit the CF guidelines for CRC screening. 
Are the methods appropriate and well described?
If not, please specify what is required in your comments to the authors.
Unable to assess
Does the work include the necessary controls?
If not, please specify which controls are required in your comments to the authors.
Unable to assess
Are the conclusions drawn adequately supported by the data shown?
If not, please explain in your comments to the authors.
No
Are you able to assess any statistics in the manuscript or would you recommend an additional
statistical review?
If  an  additional  statistical  review  is  recommended,  please  specify  what  aspects  require  further
assessment in your comments to the editors.
Not relevant to this manuscript
Quality of written English
Please indicate the quality of language in the manuscript:
Acceptable
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