Reviewer’s report
Title: 
Cervical cancer in women under 30 years of age in Norway; a population-based cohort study
Version: 
2 
Date: 
14 Jan 2021
Reviewer's report:
Thanks for the opportunity to review the revised manuscript and for responding to my comments.
Although the authors have addressed some comments sufficiently, there are still some issues that remain unresolved.
Abstract:
Please add AAPC when reporting results on TEMPORAL trends.
Also, the authors should be specific with respect to the comparison group. (For example: 
COMPARED TO WOMEN AGED 30
YEARS AND OLDER, A lower
proportion of 
women <30 YEARS were diagnosed at more advanced stages and a slightly
higher proportion were diagnosed with adenocarcinoma and adenosquamous
carcinoma
1. I appreciate that the authors had the paper reviewed by a native speaker. Unfortunately, there are still some language issues
(e.g., page 8, lines 16-18; page 9, line 1 (should read have in stead of has)
2. I appreciate that the authors have added information on Joinpoint regression, however, i don't see any information in the results
or discussion? In the first paragraph, the authors describe changes in incidence rates over time and they use proportions. It's fine to
include this, but not sufficient. The authors should use results from the joinpoint regression analysis when describing temporal
trends. Also, the authors state that average changes were calculated (page 6, line 18). When doing a joinpoint regression analysis,
you typically calculate annual percentage change (APC) and average annual percentage change (AAPC), as described in ref no. 9.
Please revise.
3. I acknowlegde that categorization of histologic subtypes were performed like it was done previously (ref no 9), however, for
transparency the authors should make it clear whether tumors with uncertainty about the originating site were excluded or not. 
I
suggest the authors to consider consulting a gynecological pathologist.
4. Page 3, line 46: please delete probably. You cannot be sure that sexual behavior is the only explanation for these findings. Please
revise and say that the underling resons for these findings remain unclear but may be explained by changes in sexual behavior,
screening history (later in your article you state that coverage has changed) etc.
5. As the authors describe changes in mortality over time it would have been interesting to report unadjusted and adjusted HR in
separate time periods as well. 
6. I appreciate that the authors state in the discussion that women <25 years are not routinely screened and report why they might
have been screened. The authors should also discuss the potential impact on study results. These numbers cannot be compared with
numbers for women of screening age, as women <25 have been screened for a reason. Maybe they had symptoms.?? Also, when
reporting the number/proportion of unscreened women above 30 it would be great to see the numbers after excluding women aged
69+ when screening is ceased. It woud expect the numbers to decline.
7. With respect to hysterectomy, i acknowlegde the authors for their work but i am still not satisfied. In a recent study (see link
below), the number of hysterectomies in Norway is quite similar to that in Denmark. Given that studies find a lifetime cumulative
risk of hysterectomy around 18-20 % in Denmark, the percentages in the paper seem off. Also, the authors should add these results
in a supplementary table for transparency. Or they should simply state that correction for hysterecotmy was not possible and state
the implications this might have (see my comments to the previous manuscript). This issue has not been addresssed sufficently.
https://tidsskriftet.no/en/2020/10/originalartikkel/hysterectomy-norway-2008-
18#:~:text=Hysterectomy%20is%20a%20common%20gynaecological%20procedure.%20No%20Norwegian,were%20used%20for%20hysterectomies%20in%20the%20period%202008%E2%80%9318.
8. Previously i urged the authors to condense the discussion where they compare to previous studies and instead discuss the
implications of the results. I don't see any major changes besides adding information on HPV vaccination(and thanks for including
this). However, i acknowlegde that we as researchers have diffierent opinion with respect to this issue so i will leave it to the
discretion of the authors and editors to decide whether any changes are needed.
9. Table 1; it is unclear on what data chi2 was performed. It seems like the authors compare across age groups and FIGO
stages/period of diagnosis combined. Is that true? Or do you for each time period compare proportions across age groups? If the
latter is correct, more p-values should be stated, If the former is correct, please add information on this in the table legend.
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Is the study design appropriate to answer the research question (including the use of appropriate controls), and are the conclusions
supported by the evidence presented?
Yes
Are the methods sufficiently described to allow the study to be repeated?
No
Is the use of statistics and treatment of uncertainties appropriate?
No
Is the presentation of the work clear?
Yes
Are the images in this manuscript (including electrophoretic gels and blots) free from apparent manipulation?
No