Reviewer ’s report  
 
Title: Mitochondrial DNA copy number in cervical exfoliated cells and risk of cervical cancer  
among HPV -positive women  
 
Version: 0 Date: 25 Nov 2019  
 
Reviewer: Annarosa Del Mistro  
 
Reviewer's report:  
 
The manuscript by Hang and collaborators reports data on a case -control study investigating the 
mitochondrial copy number (mtCN) in samples from patients with cervical cancer and matche d 
controls. They found a higher median mtCN value in cases than controls, and conclude that 
mtCN may represent a novel biomarker in cervical cancer screening.  
 
Although the number of analyzed samples is high, there are concerns on methodological issues, 
on the evaluation of the results in comparison to previous knowledge on mtCN and cancer, and 
on the effective potential of mtCN determination as a biomarker.  
 
METHODOLOGY: the mtCN determination has been performed on exfoliated cervical cells, but 
no details a re provided on the cytological diagnoses (the final cancer diagnosis was 
histologically assessed) and no considerations were formulated on the contribution of the 
different cell types on the mtCN determination. Previous studies on mtCN in cancer were based  
on tissue or blood samples. The cytological diagnoses are important for both understanding the 
results in relation to the cell sample composition, and correlating mtCN value, as potential 
biomarker, to cytology.  
 
RESULTS: the analytical results of the mtC N (i.e., copy number of mtDNA) are not reported, 
and the median and quartile mtCN values reported in Table 1 show ample overlapping between 
cases and controls. The finding of a higher median mtCN value in cases than controls is in 
contrast to data on cervi cal and other cancers in which no difference or the opposite result were 
documented [ref. 31; see also the paper by Reznik et al (eLife 2016;5:e10769), in which the 
comparison was made between matched tumor and adjacent normal tissue]. This is a relevant 
aspect and need to be adequately addressed. Some comment should also be made on the 
association between mithocondrial DNA copy number and cervical cancer reported in Table 3, in 
relation to the not linear result for the third quartile for HPV16 and other HP V types.  
 
DISCUSSION, page 9: in the comparisons with other studies, the type of sample analyzed 
should also be discussed.  
 
CONCLUSIONS: for the considerations made in the above points, the data do not support the 
conclusions.  
 
REFERENCES: volume and page num bers are missing for ref. 29.  
 
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.  
 
No 
 
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:  
 
Acceptable  
 
Declaration of competing interests  
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