White Button Mushroom Extract in Preventing the Recurrence of Breast Cancer in Postmenopausal Breast Cancer Survivors

DISEASE CHARACTERISTICS: * Meets 1 of the following criteria: * Prior diagnosis of infiltrating carcinoma of the breast ≥ 5 years prior to study entry * Prior diagnosis of ductal carcinoma in situ * No evidence of disease * Completed all cancer therapy, with the exception of reconstructive surgery, at least 6 months prior to study entry * Meets one of the following criteria: * Normal mammogram within 1 year of study entry * Underwent bilateral mastectomy and has been in remission for 5 years, as documented by an oncologist * Hormone receptor status not specified PATIENT CHARACTERISTICS: * ECOG performance status 0-1 * WBC ≥ 3,500/mm³ * ANC ≥ 1,500/mm³ * Platelet count ≥ 100,000/mm³ * Hemoglobin ≥ 9.0 g/dL * Postmenopausal, defined as any of the following: * Continuous absence of menstruation for 12+ months * Status post bilateral oophorectomy * Status post hysterectomy with follicle-stimulating hormone in menopausal range * Creatinine ≤ 1.5 times upper limit of normal (ULN) or less * Total bilirubin ≤ 1.5 times ULN * AST and ALT \< 2 times ULN * No allergy to mushrooms * No personal history of any invasive cancer, other than breast cancer, or squamous cell or basal cell skin cancer * No osteoporosis, defined as a bone-mineral density T-score of \< -2.5 on dual-energy x-ray absorptiometry scan * No major systemic infections or other major medical illnesses of the cardiovascular, respiratory, or digestive system PRIOR CONCURRENT THERAPY: * See Disease Characteristics * More than 3 months since prior and no concurrent hormone-modifying medications, including any of the following: * Oral contraceptives * Hormone replacement * Selective estrogen receptor modifiers * Other aromatase inhibitors * Gonadotropic-releasing hormone modifiers * At least 1 month since prior and no other concurrent mushroom extracts or DHEA as a dietary supplement * No concurrent therapy, except continued medications for unrelated illness that are not excluded, and necessary medications for unrelated acute illnesses that may occur during the study (e.g., cold, flu, or infection) * No more than 3 concurrent servings per week of the following foods: * Flaxseeds and flaxseed meal * High-energy bars or diet bars containing soy or soy protein * Liquid-nutrition drinks containing soy or soy protein (e.g., Odwalla Future Shake or Ensure Plus) * Miso soup * Natto * Packaged mixed dishes with soy or tofu (e.g., lasagna, burritos, or stir-fry) * Cooked soybeans or edamame (i.e., green soybeans) * Roasted soy nuts * Soymilk, regular or low-fat, plain or flavored * Soy cheese, such as cheddar, mozzarella, cram cheese, or parmesan (includes all foods made with soy cheese) * Soy protein powders (e.g., performance or body-builder powders) * Soy yogurt, all types * Soy sauce, tamari, teriyaki sauce, Szechuan sauce, or hoisin sauce * Soy ice cream, tofutti, or other soy desserts * Tempeh, all types * Tofu, all types, including low-fat, flavored, marinated, and smoked * Tofu or soy breakfast sausage, bacon, or other breakfast meat * Tofu or soy cold cuts, hot dogs, or other deli meat substitutes * Veggie soy or tofu burger, ground meat substitute (texturized vegetable protein), or soy or tofu, chicken, or turkey * Concurrent supplemental calcium and/or vitamin D and bisphosphonates allowed provided doses remain constant throughout the run-in and treatment portions of the trial