<qa>  What is the potential for aromatase expression?A pilot study of letrozole in postmenopausal women on hormone replacement therapy at high risk of developing breast cancer. Subjects will have hyperplasia with atypia or borderline Epithelial HyperplasiaAtypical Hyperplasia and evidence of Estrogen Receptor expression by random periareolar fine needle aspiration and baseline serum estradiol levels less than or equal to 150 pgml. The feasibility of performing RT-qPCR on breast specimens for aromatase expression will also be done at baseline. 