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:16 February 2011
Reviewer: Neal D Freedman
Reviewer's report:
The authors examine the association of childbearing and menarche history with
esophageal cancer in a small hospital based case-control study in Guangzhou
China.
Possible associations between menstrual and reproductive factors with
esophageal cancer are an intriguing hypothesis. However, few studies have been
performed to date. Thus, the current analysis targets an intriguing and potentially
important research question. However, the study is limited by a small sample
size and also by a cross sectional study design which could potentially be
affected by recall and selection bias.
- Major Compulsory Revisions
1. It is very important for the authors to distinguish esophageal cancers by
histological type. In China, nearly all esophageal cancers have a squamous
histology. In Western countries, however, esophageal adenocarcinoma is more
common. The authors should acknowledge that risk factors for these two cancers
are very different. For example, alcohol is a strong cause of esophageal
squamous cell carcinoma, but not esophageal adenocarcinoma. Obesity, on the
other hand, substantially increases adenocarcinoma risk but has little to no
association with squamous cancer risk.
The authors should specify the histology of cancers in their study.
More importantly, the authors should restrict their discussion of previous studies
to those of esophageal squamous cell carcinoma.
2. The sex-ratio varies substantially by geographic region and histologic type.
The highest sex ratio has been seen for esophageal adenocarcinoma in Western
countries. Incidence rates for esophageal squamous cell carcinoma are more
similar in both sexes, though higher in men than women in many populations.
But, in several parts of China with extremely high rates of esophageal cancer, the
sex ratio is nearly 1:1. What is the sex ratio in Guangzhou, China? The authors
should provide specific data about incidence rates in the region of the current
study. Are a similar proportion of male and female patients diagnosed at the
hospital and treated? In some parts of the world, men with esophageal cancer
are more likely to receive a hospital diagnosis and treatment than women with
esophageal cancer.
3. How were the categories for analysis, in Table 2, chosen? For example, there
are very few cases and controls in the oldest category of age at first birth. The
first and third categories of age at menarche and age at menopause are also
very small. Since the first category of age at menarche and age at menopause
serves as the referent group, small numbers in this group leads to instability in
the risk estimates. The authors should create tertiles or quartiles based on the
controls for these variables. Categorizing the exposures in this way will increase
the precision of the risk estimates. It is especially important due to the small
sample size of the current study.
Also, could the authors analyze years of menstruation? (age at menopause –
age at menarche)
4.Where the authors able to collect additional information on other related
exposures such as types and duration of contraceptive use (i.e oral
contraceptives, IUD), hysterectomy and oophorectomy, breast feeding, or
menopausal hormone therapy?
"Minor issues not for publication"
1. Conclusions, first paragraph, replace "firs" with "first"
2. Abstract, Background, "is still lacked" should be "is still lacking"
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.