Association of overweight and obesity with breast cancer in India: scope for improvement.

Sir,

A case-control study which was carried out by Singh et al.,(1) titled “Association of overweight and obesity with breast cancer in India.” It was concluded that overweight and obese women had odd's ratio of 1.06 and 2.27, respectively, as compared with women with normal weight. Obesity is a well-known risk factor for postmenopausal breast cancer. Numerous epidemiologic studies have reported positive associations between obesity and breast cancer risk among East Asian women.(2345) Objective of this article is to address some limitations that should be considered when interpreting their results of case-control study.

Some of the notions by Kenneth and David(6) guide investigators who do or readers who assess case-control study. First, in the present study authors have explicitly defined the criteria for diagnosis of a case of breast cancer but not very clear about geographic distribution of cases. However, this is an important eligibility criteria used for selection of cases. Second control should come from same population as the cases and their selection should be independent of the exposure of the interest. In the present study, it is documented that 320 normal healthy individuals accompanying the patients in the Department of Gastroenterology, Medicine and Surgery at All India Institute of Medical Sciences, New Delhi, and at Comprehensive Rural Health Services Project at Ballabgarh Hospital, Faridabad, Haryana, constituted the control group. In this study, it is not very clear about criteria used for labeling any individual healthy or free from breast cancer. Third, investigators should blind the data gathers to the case or control status of participants or, if impossible, at least blind them to the main hypothesis of the study. To overcome biases, it is necessary to use some blinding technique. Authors failed to address confounding in this study at design stage. It also reveals that care of confounding can be taken care with analytical techniques; there were no paired data in the present study; however, paired “t” test was utilized. It point out that care of confounders can be taken care with proper analytical techniques such as logistic regression analysis or stratified analysis such as Mantel-Haenszel approaches.(6)

Devotions of meticulous attention to these points enhance the validity of the results and bolster the reader's confidence in the findings. This issue needs to be address and optimum precaution to be taken while selecting controls.

As a reader if I assess, I find only comparative information. I do not find adequate discussion about obesity and carcinogenesis. This is very important as a reader's point of view. As the basis for understanding the potential mechanism of obesity and cancer relationship has advanced, numbers of new hypotheses have emerged. The adipocytokines are a complex group of biologically active polypeptides.(78)

Leptin is a growth hormone, secreted by adipose tissue, whose levels are normally elevated in obese individuals and may have a promoting effect on carcinogenesis and metastasis of breast cancer, possibly in an autocrine manner.(910)

This study has some limitations that should be considered when interpreting their results. First, because they did not have updated information on menopausal status, which would modify the association between body mass index/weight change and breast cancer, the possibility of misclassification of menopausal status at breast cancer onset should be considered. Such misclassification would be problematic in premenopausal women, since recently menopausal women would be misclassified as premenopausal during the follow-up period. Such misclassification could partly explain the inconsistent results from several studies of the association between body size and breast cancer among premenopausal women. Studies of younger women with updated information on menopausal status should be initiated among premenopausal women. However, this limitation is a minor concern for postmenopausal women.