Statement: presence of hot flashes for at least 40 years prior to study registration is required for all patients that want to participate in the primary trial or the secondary trial.
Primary_evidence: DISEASE CHARACTERISTICS:   Women with a history of breast cancer (currently without malignant disease)   Bothersome hot flashes (defined by their occurrence  28 times per week and of sufficient severity to make the patient desire therapeutic intervention)   Presence of hot flashes for  30 days prior to study registration   Willingness to provide the biologic specimens as required by the protocol   Hormone receptor status not specified   PATIENT CHARACTERISTICS:   Women who are postmenopausal as defined by absence of a period in the past 12 months or bilateral oophorectomy   Women with at least one ovary but without a uterus should be deemed postmenopausal by either age over 55 or a combination of estrogen within a postmenopausal range (per local lab) and FSH over 40 mIU/mL   No women of childbearing potential or who are premenopausal   Creatinine clearance > 30 mL/min   Ability to complete questionnaire(s) by themselves or with assistance   ECOG performance status 0 or 1   No history of allergic or other adverse reaction to magnesium   No diabetes   No patients with conditions that are implicated in decreased absorption of magnesium (e.g., Crohn disease, ETOH abuse)   No patients who have diarrhea where magnesium might make it worse (per provider discretion)   PRIOR CONCURRENT THERAPY:   None of the following current ( 28 days prior to registration) or planned therapies (tamoxifen, raloxifene, or aromatase inhibitors are allowed, but the patient must have been on a constant dose for  28 days and must not be expected to stop the medication during the study period):   Antineoplastic chemotherapy (trastuzumab or lapatinib are allowed)   Androgens   Estrogens (any delivery route)   Progestational agents   No prior use of magnesium for hot flashes   No current or planned use of gabapentin (for any reasons) or antidepressants (for any reasons) or other agents for treating hot flashes (except stable dose of vitamin E is allowed as long as it was started > 30 days prior to study registration and are to be continued through the study period; soy is allowed, if it is planned to be continued at the same dose during the study period)   No current use of magnesium for any indication (except one standard multiple vitamin dose is allowed per day)   Not taking diuretics, corticosteroids, bile acid sequestrants, and other prescription and over-the-counter medications that may affect magnesium levels   No current ( 7 days prior to registration) or planned use of other non-drug therapies for managing hot flashes, such as acupuncture or yoga (use of these therapies for other reasons is allowed)
Secondary_evidence: Inclusion Criteria:   female patients, >=18 years of age, with locally advanced breast cancer. Exclusion Criteria:   previous therapy for any invasive malignancy.