Reviewer's report
Title:Phytoestrogen consumption from foods and supplements and ovarian
cancer risk: a population-based case control study
Version: 1Date:25 July 2011
Reviewer: Michelle Cotterchio
Reviewer's report:
Major Revisions:
Concerns with this paper that the authors should address are listed below:
- The Abstract (background section) indicates possible “detrimental effects” of
phytoetrogens as regards ovarian cancer risk; however, it is not clear where this
statement comes from since the authors review of the literature in the Discussion
section mentions only studies that found a protective effect or no association (a
positive finding is never referenced). Either expand upon the “detrimental” info
(and support with references), or delete this statement from the Abstract. Also,
expand upon and substantiate this statement in the Background section, or
remove the sentence (para 3, line 3 of Background section).
- Abstract (results section) should first state that “no statistically significant
findings were observed”…. and then go on to mention the “suggested inverse
associations of borderline significance”.
- Similarly, the first paragraph of Discussion should be re-worded so as not to
over-interpret findings. (example of re-wording: “Although no statistically
significant associations were observed for isoflavone, lignan, and total PE and
ovarian cancer risk, we did find a suggestion of……….”.
- Abstract (conclusion section) should replace “increases” with “was associated
with”; this is because there was no statistically significant increased nor
decreased association observed so why the focus on increased? Would now
read: ” we found no evidence that PE consumption was associated with ovarian
cancer risk”.
- This study seems underpowered as there are only 200 cases and 390 controls;
could some mention of power be added to the Discussion section.
- The overall response rate is less than 50% for cases, and 40% for controls.
What efforts were made to improve participation? Details should be provided in
the Methods section – for example, how many follow-up reminder calls were
made per subject? Was the FFQ re-mailed to non-responders?
- The poor response rate is a limitation of this study (and this should not be
dismissed). The addition of a Table that includes the distribution of known
risk/protective factors for ovarian cancer among cases and controls would be
helpful; please include N (%) for cases and controls separately, and age-adjusted
OR.
- More details are needed in the Methods regarding how various phytoestrogen
variables were derived. What is included in total PE – is it all isoflavone and all
lignans?
- Why were the phytoestrogen variables calculated as “mcg/1000 kcal” versus
“mcg/day”?
- Is the content of foods found in Ontario likely to be similar to that in NJ? Some
comment on this should be added.
- How were potential confounders assessed for this datasaet? How was it
decided what remained in the final model? (or were some variables just assumed
to be confounders?) This needs to be explained in the Methods section. Given
the limited power of this study, the most parsimonious model would be preferred
(ie., that with all identified confounders only).
- Why was family hx of ovarian cancer not considered as a possible confounder?
- How might future case-control studies be improved to adequately assess
phytoestrogen intake and ovarian cancer risk? Some discussion of this would be
warranted in the Conclusion section.
- Table 3 should be added to Table 2 (ie., combined into one long table). Why is
it necessary to do a separate Table for Lignans? (especially when total PE is in
the other table, and this includes lignans, right?)
- List of supplements assessed could be added to the Appendix table that
includes additional food items currently.
Level of interest: An article of importance in its field
Quality of written English: Needs some language corrections before being
published
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
'I declare that I have no competing interests'