Intermittent Letrozole Therapy in Postmenopausal Women With Metastatic Breast Cancer

Treatment is intermittent with possible breaks between each 28 day treatment cycle if CA 15-3 or CA 27.29 level that has decreased by at least 50% of that individual patient's baseline or peak level on firstline letrozole or anastrozole therapy or has decreased into the normal reference range per institutional parameters. Letrozole or anastrozole therapy will be interrupted until CA 15-3 or CA 27.29 levels rise by at least 25% above trough CA 15-3 or CA 27.29 level. If the trough level is in the normal reference range then the CA 15-3 or CA 27.29 must rise into the normal reference range.