Reviewer’s report
Title: 
Cervical cancer in women under 30 years of age in Norway; a population-
based cohort study
Version: 
0 
Date: 
28 May 2020
Reviewer's report:
Thank you for the opportunity to review the paper entitled "Cervical cancer in
women below 30 years of age in Norway".
The authors describe trends in cervical cancer incidence by age and over
calendar time in Norway, focusing on differences between women below 30 and
aged 30 years and older. The authors report an increase in cervical cancer
incidence among women <30 years but that most cases are diagnosed at an early
stage and is associated with a fairly good prognosis.
I find the topic interesting and important. However, the paper needs a major
revision before it can be published. Furthermore, the paper would benefit from
being reviewed by a native speaker to improve the language. Be specific when
describing results! For example, you don't report mortality 
- but risk of cervical
cancer death….
Major comments:
1. It is now well known that cervical cancer incidence rates should be corrected
for hysterectomy incidence (or prevalence), as failure to do so will likely
underestimate the "true incidence rates". This is particularly important because
most countries report a decline in hysterectomy incidence rates over calendar
time. Although I acknowledge that the hysterectomy incidence is probably very
low in the youngest women and correction for hysterectomy likely has no
impact, correction for hysterectomy is important for women aged 30 years and
older. 
Minor comments:
Material and Methods
2. Material and Methods would benefit from more structure; setting, study
population, registries (I assume that information on prior screening is retrieved
from another registry. Not much is stated about cause of death registry) etc. I
would also like information on the validity of the registries - especially the cause
of death registry. As I am aware that linkage across registries is likely performed
using a personal identification number not all readers will know this. Please add
more information.
3. I am not familiar with the method used for calculating cumulative risk of
death. Why not use a simple Kaplan Meier? What is the rationale behind their
decision? It would be interesting to add stage-stratified curves to the figures….
4. Why did you censor at age 75 and after 15 years of follow-up? The rationale
behind this decision is unclear. 
5. With regards to FIGO stage and morphology - did you have information about
this for all cases? In most cancer registries, this is not the case - particularly in
the 1950'es-1970'es. Please add more information
6. With regards to screening, most studies exclude smears collected within 3-6
months of diagnosis as they are usually regarded as part of the diagnostic work-
up and not screening. Please make a sensitivity analysis.
7. I suggest to do some kind of trend analysis in incidence rates, for example
joinpoint regression or something similar. This would provide important
knowledge on whether the increase in cervical cancer incidence among the
youngest women was statistically significant.
Results
8. I don't find results on unadjusted and adjusted HR (only mentioned in the
text). More information is needed. I suggest to make a table.
9. The authors should explore in greater detail why the incidence rate is
increasing among the youngest women. For example is there an increase in the
proportion of unscreened women over time? Also, I would be curious to know if
there is a difference in the proportion of women with FIGO I over time.
10. I suggest to add calendar time to Table 1
11. I don't see any figure legends ?? Figures and tables should be self-
explanatory. More information is needed, particularly for Figure 2. It is unclear if
the cumulative risk is adjusted or unadjusted.
Discussion
1. The authors primarily compare their trends in incidence rates to other studies,
which is also important, but the section is too long. They could shorten it up and
add more about the topics mentioned above and below. If some things/results
remain unclear or unexplained, the authors should simply state that further
studies are needed.
2. I find it interesting that the gap in cumulative risk of death declines over time.
I'd like the authors to elaborate and discuss this more. Is it because the
proportion of women aged 30+ with FIGO1 is increasing over time? Is it
because more women are attending screening?
Are the methods appropriate and well described?
If not, please specify what is required in your comments to the authors.
No
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.
I recommend additional statistical review
Quality of written English
Please indicate the quality of language in the manuscript:
Needs some language corrections before being published
Declaration of competing interests
Please complete a declaration of competing interests, considering the following
questions:
1
. 
Have you in the past five years received reimbursements, fees, funding, or
salary from an organisation that may in any way gain or lose financially
from the publication of this manuscript, either now or in the future?
2
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Do you hold any stocks or shares in an organisation that may in any way
gain or lose financially from the publication of this manuscript, either now
or in the future?
3
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Do you hold or are you currently applying for any patents relating to the
content of the manuscript?
4
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Have you received reimbursements, fees, funding, or salary from an
organization that holds or has applied for patents relating to the content of
the manuscript?
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Do you have any other financial competing interests?
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Do you have any non-financial competing interests in relation to this
paper?
If you can answer no to all of the above, write 'I declare that I have no competing
interests' below. If your reply is yes to any, please give details below.
I declare I have no compteting interests
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