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Displaying 1-2 out of 2 published
19 November 2013
We read with interest the article by Mackenzie et al.1 The authors reported that of the exposed cohort of 28,032 patients, 5078 patients (18.1%) had already received spironolactone for the first time before the index date. On the other hand, the number of patients who had received sprinolactone before the index date in the control group (total number: 55,961) was not mentioned in the article. The proportion of the first exposure before the index date in the exposed group was relatively high (18.1%), and could not be overlooked. The difference of this proportion between the two groups is a concern in evaluating a true impact of the exposure of spironolactone on the breast cancer in women over 55 years. Although the authors may have regarded the exposure before the index date as a negligible factor, it is difficult to deny the possibility that early exposure to spironolactone (i.e., before 55 years) promotes latent growth of breast cancer considering its longitudinal hormonal effect. We would appreciate it if the authors could address the following points: the number and the proportion of patients who had received sprinolactone before the index date in the control group; the difference of this covariate between the two groups; and an effect of this covariate on breast cancer incidence in women over 55 years. If this covariate is identified as significant factor, it would be favorable to enter it into a model set for estimation of the risk of spironolactone.
We are also interested in the ethnic distribution in this study. Susceptibility to breast cancer itself is known to be ethnically different.2 Furthermore, ethnic differences of polymorphism in spironolactone-metabolizing enzymes can influence the hormonal effects of spironolactone and its active metabolites.3 For this reason, ethnic distribution might have affected the results in this study as well.
1. Mackenzie IS, MacDonald TM, Thompson A, Morant S, Wei L. Spironolactone and risk of incident breast cancer in women older than 55 years: retrospective, matched cohort study. BMJ. 2012;345:e4447.
2. DeSantis C, Siegel R, Bandi P, Jemal A. Breast cancer statistics, 2011. CA: A Cancer Journal for Clinicians. 2011;61:408-18.
3. Karim A. Spironolactone: disposition, metabolism, pharmacodynamics, and bioavailability. Drug metabolism reviews. 1978;8:151-88.
Competing interests: WH has received research funding from the Ministry of Health, Labour and Welfare of Japan, Teika Seiyaku, Takeda Pharmaceuticals, Mochida, Pfizer, Asteras and Daiichi Sankyo, and lecture fees from Pfizer, Acterion, Novartis, Daiich Sankyo, GlaxoSmithKline and Nihon Shinyaku.
Pharmaceuticals and Medical Devices Agency, 3-3-2, Kasumigaseki, Chiyoda-ku, Tokyo
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18 July 2012
Author themselves stated that smoking, age at menarche, age at first child, age at menopause, parity are the risk factors for breast cancer but they were not considered in calculation of propensity score for matching as co-variates whereas so many other factors were considered. I am not clear about this.
Competing interests: None declared
Indian Council of Medical Research, Ansari Nagar, New Delhi-110029
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