Review for 10.1186/1471-230X-11-49 (2011)

Reviewer's report
Title:Reproductive factors and oesophageal cancer in Chinese women: a
case-control study
Version: 1Date:11 February 2011
Reviewer: Martin Rutegård
Reviewer's report:
Chen and colleagues have conducted a hospital-based case-control study in
Guangzhou, China from Jun 2006 to May 2009 with 73 cases and 157 controls.
The exposure was defined as various reproductive factors in women whereas the
outcome was newly diagnosed oesophageal cancer. In general, the study is
coherent and mainly well-written (although the English might need some
refinement) but is definitely lacking in details concerning the methodology. The
topic is interesting, but substantial novelty is unfortunately lacking as this series
too is small and also potentially influenced by selection bias as it can hardly be
called population-based.
# Major Compulsory Revisions
1) In the background, it needs to be emphasised that the risk factors for
squamous cell cancer and adenocarcinoma are different and that the sex
difference is mainly observed for the latter type. The growing incidence of
adenocarcinoma but not squamous cell carcinoma also needs to be mentioned.
2) It also needs to be mentioned that the sex difference is age-related, as
suggested by Derakhshan et al 2009 Gut and Rutegard et al 2010 European
Journal of Cancer. Furthermore, there is ample evidence that risk factors do not
seem to be distributed in a skewed fashion between the sexes, as suggested by
Lindblad et al 2006 Cancer Causes and Control.
3) Furthermore, there is a pertinent recent meta-analysis on reproductive factors
that needs to be included and commented in the introduction and the discussion:
Cronin-Fenton et al 2010 European Journal of Cancer.
4) In the methods, it needs to stated what if every type of cancer warranted
exclusion from the study; specifically, various types of skin cancers such as basal
cell carcinoma and squamous cell cancers might not be a reason to exclude
those patients, as these more benign tumours might not influence selection. It
might be helpful also to make clear whether controls were included if they ever
had suffered from cancer. There is also a need to state why only 2 controls were
picked, as opposed to the standard 4-5 per case.
5) I would certainly like to see data on breastfeeding as well, as this previously
has been showed to be the only determinant influencing oesophageal
adenocarcinoma risk. If this information is not available, this might turn out be a
major disadvantage to this study.
6) In the methods, it should also be clearly stated whether the performed tests
were predefined, what reasons prompted the chosen cut-offs in exposure
categories. There is a certain risk of multiple testing and one gets the impression
that the authors are out on a "fishing expedition".
7) In results, the distribution of adenocarcinoma and squamous cell carcinoma
needs to be added.
8) The stratified analysis in the discussion must be mentioned in the methods
section; for now, it seems to have appeared magically.
# Minor Essential Revisions
1) In table 1, it would be much preferable to include a column with p values
(instead of just stating "p < 0.05" or not).
2) In the discussion, I would like to see a more refined discussion about the
consequences of choosing controls from a cohort not randomly selected. There
is a certain risk that people seeking routine health examination may be more
afflicted by risk factors than the general population, and any bias this may pose
must be at least commented upon.
3) It must be an understatement to claim that "...the two histological types... may
differ in etiology to some degree". There are substantive differences, e.g. shown
by Lagergren et al 1998 NEJM and Lindblad et al 2005 Cancer Causes and
Control. This needs to be revised accordingly.
4) Linguistic check is needed.
# Discretionary Revisions
Level of interest: An article whose findings are important to those with closely
related research interests
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.