P-189

Abstract

Background: Breast cancer (BC) is the primary cause of cancer deaths among women in Mexico. Our previous work has shown associations between BC and arsenic (As) and phthalate exposure, respectively, in Mexican women.Objectives: To explore whether environmental exposure to As and phthalates interact in their association with BC.Methods: A total of 233 cases with incident BC and 221 controls (matched to cases by age and state) were recruited as part of an ongoing case-control study in 5 states in northern Mexico. Reproductive history, sociodemographic, and anthropometric data were collected using questionnaires and physical measurements. Concentrations of creatinine, 9 phthalate metabolites, and speciated As were measured from first-morning void samples. As methylation capacity was assessed by the primary (PMI) and secondary (SMI) methylation indices: [monomethylarsonic acid]/[As(III)+As(V)] and [dimethylarsinic acid/monomethylarsonic acid], respectively. Logistic regression was used to estimate odds ratios comparing high (> median) to low (≤ median) levels of phthalate metabolites and indices of As methylation capacity (IAMC). Likelihood ratio tests were used to test for interaction.Results: Statistically significant (p<0.20) sub-multiplicative interaction in the association with BC was identified for the following exposures: 1) the PMI and mono-(3-carboxypropyl) phthalate, 2) the PMI and mono-(2-ethyl-5-hydroxyhexyl) phthalate, and 3) the SMI and monobenzyl phthalate.Conclusions: Biological data are necessary to determine whether these findings are related to a common pathway in the metabolism of these exposures that alters BC risk.