Reviewer's report
Title:Phytoestrogen consumption from foods and supplements and ovarian
cancer risk: a population-based case control study
Version: 1Date:28 July 2011
Reviewer: Paolo Toniolo
Reviewer's report:
This report concerns a thoroughly described and competently analyzed
population-based case control study of phytoestrogen intake in association with
the risk of epithelial ovarian cancer.
Although the study is well performed, its limitations, which the authors consider
carefully, are worrisome. The most glaring is that the target population is hardly
the ideal one because of the very limited exposure to small amounts of
phytoestrogens, which, along with the inevitable errors in estimates of
consumptions, drastically reduces statistical power. The second one is the poor
response rate, especially serious among the controls, which might have had
hard-to-assess impact on the associations of interest. Nevertheless, given the
paucity of research on ovarian cancer, the suggestion of a possible reduced risk
even in light of the above limitations remains intriguing.
Major Compulsory Revisions
1. Background. The authors do not propose a specific hypothesis concerning the
direction of the association. Judging from the evidence provided, limited evidence
in the literature is mixed, although a prevailing interpretation is that of a reduced
risk. In the absence of a clear guiding hypothesis the study might be considered
too small and lacking adequate statistical power.
2. Methods, end of first para. The figure of 47% respondent cases is misleading
given that 205 returned the FFQ and were considered in statistical analyses. The
actual figure should be 41.5%. Likewise, the similar figure of 40% respondent
controls is equally misleading, as it does not take into account those who
returned the FFQ. Not all numbers of eligible controls are provided (those
identified through the CMS are not listed) so that a reader could not verify the
actual percent respondents. However, the figure is certainly well below 40%. The
sentence must be rewritten in order to convey the actual figures – not a trivial
omission.
3. In light of the above considerations, more emphasis should be given in the
discussion section on the possible implications from the unfortunately low, and
likely inevitably so, response rate, which is well below 50%.
Minor Essential Revisions
4. Background, 1st para. It is true that OCs and parity are major protective
factors, but it seems necessary to mention the prominent role of chronic
inflammatory processes, also considering that the proliferating stimuli of the
non-steroidal estrogens in question might have a substantial influence the latter.
The strong protection observed for tubal ligation, which is in accord with the
literature, also suggests that the issue could not be ignored.
5. Discussion, last sentence. The obvious should not be stated. It is
recommended that the sentence be deleted.
6. Abstract, last sentence. Stating that findings need replication is an obvious
part of scientific inquiry, therefore unnecessary.
7. Methods, 2nd paragraph and later, “years of age” is poor English – “older than
21” should suffice.
Discretionary Revisions
8. In both Abstract and Introduction ovarian cancer should be defined as
“epithelial”, given the substantial pathological, clinical and epidemiological
differences between the two main entities. Whether or not this should be stated
in the title is a matter of discretion by the authors. Later on in the paper, once the
characteristic of the type of cancer of interested are established it would be
irrelevant to repeat.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
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