Plaza-Díaz J, et al. - In this case-control clinical study that will be conducted to determine if there is a relation between breast cancer risk and the composition and functionality of the mammary/gut microbiota and exposure to environmental contaminants (endocrine disruptors, EDCs) might change these microbiota. Participants will be women between 25 and 70 years of age, with cases defined as women diagnosed and surgically intervened of breast cancer (stages I and II), excluding those with antecedents of cancer or advanced tumor stage (metastasis), or who have had antibiotic therapy within a period of 3 months before recruitment, or any neoadjuvant therapy. This inquiry would be the first-ever attempt to look at breast cancer risk in relation to contributions from bacteria, archaea, viruses and fungi together with their alteration by environmental contaminants, both in the same study. The findings of this study would help clarify risk factors, improve prognosis, and contribute to introduce new intervention studies in this disease.