Exemestane in Preventing Cancer in Postmenopausal Women at Increased Risk of Developing Breast Cancer (ExCel)

At increased risk of developing breast cancer, due to at least one of the following risk factors: Gail score ≥ 1.66 Age ≥ 60 years Prior atypical ductal hyperplasia, lobular hyperplasia, or lobular carcinoma in situ on breast biopsy Prior ductal carcinoma in situ (DCIS) treated with total mastectomy with or without tamoxifen (tamoxifen must have been completed ≥ 3 months prior to randomization) No prior DCIS treated with lumpectomy with or without radiation No prior invasive breast cancer Not BRCA1 or BRCA2 carriers PATIENT CHARACTERISTICS: Previous: 35 and over Female Postmenopausal, defined as one of the following: over 50 years of age with no spontaneous menses for at least 12 months before study entry 50 years of age or under with no menses (spontaneous or secondary to hysterectomy) for at least 12 months before study entry AND with follicle-stimulating hormone level within postmenopausal range Underwent prior bilateral oophorectomy No other malignancies within the past 5 years except adequately treated nonmelanoma skin cancer, curatively treated carcinoma in situ of the cervix, or other curatively treated solid tumors with no evidence of disease for ≥ 5 years No uncontrolled hypothyroidism or hyperthyroidism No major medical or psychiatric illness (including substance and alcohol abuse within the past 2 years) that would preclude study participation or compliance Must be accessible for treatment and follow-up Willing to complete quality of life questionnaires in either English or French Current: MAP.3 participants who were randomized to the exemestane arm, are currently receiving exemestane as part of the MAP.3 study and who have not completed 5 years of exemestane. OR MAP.3 study participants who were randomized to the placebo arm and who have either completed 5 years of study drug or who are still receiving placebo. Note: this applies only to centres that choose to allow placebo "cross-over". PRIOR CONCURRENT THERAPY: Previous: More than 3 months since prior and no concurrent hormone replacement therapies More than 3 months since systemic estrogenic, androgenic, or progestational agents More than 3 months since prior and no concurrent hormonal therapies, including, but not limited to the following: Luteinizing-hormone releasing-hormone analogs (e.g., goserelin or leuprolide) Progestogens (e.g., megestrol) Prolactin inhibitors (e.g., bromocriptine) Antiandrogens (e.g., cyproterone acetate) Selective estrogen-receptor modulators (e.g., tamoxifen, toremifene, or raloxifene) No investigational drug within 30 days or 5 half lives prior to randomization No concurrent endocrine therapy No concurrent estrogens, androgens, or progesterones Concurrent low dose (≤ 100 mg/day) prophylactic aspirin allowed Concurrent bisphosphonates for prevention or treatment of osteoporosis allowed No other concurrent medications that may have an effect on study endpoints Current: There are no prior concurrent therapy restrictions for the amended MAP.3 study.