- Postmenopausal women with primary invasive breast cancer, histologically confirmed by core needle (or incisional biopsy), whose tumors are estrogen (ER) and/or progesterone (PgR) positive. Estrogen- and/or progesterone-receptor positive disease based on 10% or more nuclear staining of the invasive component of the tumor. Patients may have bilateral or multifocal invasive breast cancers. The patient may have concurrent DCIS in either breast but the DCIS will not be measured as part of the study endpoints.