Randomized Double-Blind Phase II Trial of Baby Exemestane Versus Baby Tamoxifen in Post-Menopausal Women at High Risk for Breast Cancer

Inclusion Criteria: * Postmenopausal state is defined⁸ as no menses for 12 months without an alternative medical cause. A high follicle stimulating hormone (FSH) level in the postmenopausal range may be used to confirm a post-menopausal state in women not using hormonal contraception or hormonal replacement therapy. * Any of the following criteria must be met: * Recent (within 12 months from date of consent form signature) histologic diagnosis of ER+ve (\>5%) DCIS (patients with DCIS should have undergone breast-conserving therapy i.e. lumpectomy to remove the tumor with negative surgical margins followed by radiotherapy (see footnote 1 below)) diagnosis within 3 years of HRL (ADH, LCIS, ALH), or; * At least 3% breast cancer risk at 5 years (or 5% risk at 10yrs) per one of the following risk models: the Breast Cancer Surveillance Consortium risk calculator V3 or Tyrer-Cuzick model V8 or; * Known carriers of a germline pathogenic/likely pathogenetic variant in the following moderate penetrance genes (CHEK2 or ATM), or women with chest wall irradiation before age of 30 years * Eastern Cooperative Oncology Group - Performance Status (ECOG-PS) 0-1 * Able to swallow oral medications * Participants with a prior or concurrent malignancy whose natural history or treatment does not have the potential to interfere with the safety or efficacy assessment of the investigational regimen are eligible for this trial. Specifically, all cancers diagnosed since 3 years or longer except …