5-(Chloromethyl)-α1,α1,α3,α3-tetramethyl-1,3-benzenediacetonitrile (Anastrozole EP Impurity I) is an impurity of Anastrozole (A637425), an aromatase inhibitor which functions as an antineoplastic (1,2). Anastrozole is used i post-menopausal women with advanced breast cancer.
