Reeves KW, et al. - In this nested case-control study within the Women’s Health Initiative (WHI) prospective cohort, researchers assessed the association between urinary phthalate biomarker concentrations and postmenopausal breast cancer risk. They matched controls 2:1 to cases on age, enrollment date, follow-up time, and WHI study group. They estimated 13 phthalate metabolites and creatinine in 2 or 3 urine samples per candidate over 1-3 year. They used multivariable conditional logistic regression analysis to determine odds ratios and 95% confidence intervals for breast cancer risk linked to each phthalate biomarker over up to 19 years of follow-up and observed no correlation between them. In conclusion, phthalate biomarker concentrations did not create an increased risk of developing invasive breast cancer.