Ursin G, Palla SL, Reboussin BA, Slone S, Wasilauskas C, Pike MC, Greendale GA. Post-treatment change in serum estrone predicts mammographic percent density changes in women who received combination estrogen and progestin in the Postmenopausal Estrogen/Progestin Interventions (PEPI) Trial. J Clin Oncol. 2004 Jul 15; 22(14):2842-8.