Analysis of population characteristics related to the total effective xenoestrogen burden: A biomarker of xenoestrogen exposure in breast cancer 5 Mariana F. Fernandez a, *, Loreto Santa-Marina b , Jesus M. Ibarluzea b , Jose Exposito c , Juan J. Aurrekoetxea b , Pablo Torne d , Juan Laguna e , Ana I. Rueda d , Vicente Pedraza f , Nicolas Olea a,f a Laboratory of Medical Investigations, San Cecilio University Hospital, University of Granada, 18071 Granada, Spain b Department of Health Guipuzkoa, San Sebastian, Basque Country, Spain c Department of Oncology, Virgen de las Nieves University Hospital, Granada, Spain d Department of Surgery, San Cecilio University Hospital, University of Granada, Granada, Spain e Department of Health, Granada, Spain f Department of Radiotherapy, San Cecilio University Hospital, University of Granada, Granada, Spain ARTICLE INFO Article history: Received 18 November 2006 Received in revised form 2 March 2007 Accepted 6 March 2007 Keywords: Environmental oestrogens Biomarker of exposure Breast cancer Risk factors Epidemiology ABSTRACT To analyse the link between breast cancer and the combined effect of environmental xenoes- trogens, we developed, standardised and applied a biomarker of exposure to assess the total effective xenoestrogen burden (TEXB) in human adipose tissue in a case–control study. Environ- mental oestrogens (TEXB-alpha) are separated from endogenous oestrogens (TEXB-beta), and the combined oestrogenic effect is determined from its proliferative effect (E-Screen assay). The aim of the study was to identify potential confounders, effect modifiers or other covariates associated with higher TEXB levels. In cases, age, family history of breast cancer, lactation expe- rience and smoking were associated with TEXB-alpha. In controls, only age was associated with TEXB-alpha levels. In cases, age, educational level, age at menarche, menopausal status, marital status, lactation experience and smoking were associated with TEXB-beta. In controls, only menopausal status was significantly associated with TEXB-beta levels. In conclusion, TEXB, as a biomarker of exposure, takes account of environmental, dietary, lifestyle, genetic and reproductive factors, which are not usually systematically measured across studies. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Attempts have been made to explain geographical differences in breast cancer incidence in terms of genetic, reproductive and environmental factors, but a conclusive explanation has yet to be achieved. 1 Spain has a low breast cancer incidence in comparison with other European countries, although it has shown an increase in the past few decades. 2,3 Higher breast cancer risk has been associated with conditions imply- ing a greater lifetime cumulative exposure to oestrogens, e.g. age, early menarche, late menopause, nulliparity, late first full-term pregnancy and lack of breast feeding. 1 Some soci- 0959-8049/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ejca.2007.03.010 5 Supported by grants from the Spanish Ministry of Health (FIS 00/543 and 02/1314) and the European Union Commission (EDEN: QLK4- 2002-00603, and CASCADE: Food-CT-2004-506319). * Corresponding author: Tel.: +34 958 24 2864; fax: +34 958 24 9953. E-mail address: marieta@ugr.es (M.F. Fernandez). EUROPEAN JOURNAL OF CANCER 43 (2007) 1290 – 1299 available at www.sciencedirect.com journal homepage: www.ejconline.com