Turkey Tail Mushroom for Treating Post-Menopausal Women With HER2-Negative ER-Positive Breast Cancer Undergoing Surgery

This phase II trial tests how well turkey tail mushroom (TTM) works in treating post-menopausal women with HER2-negative, estrogen receptor (ER)-positive breast cancer undergoing surgery. TTM is a common mushroom. In traditional Chinese medicine, it is used for enhancing function and removing toxins, as well as for cancer, hepatitis, and infections. There is previous evidence of significant tumor shrinkage occurring in the 2-month window between diagnosis and surgery in women who have taken TTM. Giving TTM may be effective in treating post-menopausal women with HER2-negative, ER-positive breast cancer undergoing surgery.

Inclusion Criteria: * Women ≥ 18 years of age * Histological confirmation of ER+, HER2- breast cancer, newly diagnosed and tissue available for central confirmation of Ki-67 measurement. Subjects are eligible if they have a Ki-67 of ≥10%. Ki-67 will be repeated for patients who have had this done externally. * Scheduled for definitive breast surgery * Detectable disease as defined by mammography, breast ultrasound of greater than 5mm in size. * NOTE: Tumor lesions in a previously irradiated area are not considered measurable disease; Disease that is measurable by physical examination only is not eligible * Post menopausal as defined by: * Self-reported last menstrual period greater than 12 months, or * Bilateral oophorectomy, or * Follicle stimulating hormone (FSH) \>20 mIU/mL, and estradiol level ≤ 20 pg/mL * Not taking aromatase inhibitor or a selective estrogen receptor modifier * Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0, 1 or 2 obtained ≤ 90 days prior to registration * Platelet count ≥ 100,000/mm\^3 (obtained ≤ 90 days prior to registration) * Absolute neutrophil count (ANC) ≥ 1,000/mm\^3 (obtained ≤ 90 days prior to registration) * Hemoglobin ≥ 11 g/dL (obtained ≤ 90 days prior to registration) * Serum transaminase \[alanine aminotransferase (ALT) or aspartate aminotransferase (AST)\] ≤ 1.2 x upper limit of normal (ULN) (obtained ≤ 90 days prior to registration) * Alkaline phosphatase ≤ 1.2 x ULN (obtained ≤ 90 days prior to registration) * Serum creatinine ≤ 1.2 x ULN (obtained ≤ 90 days prior to registration) * Provide written informed consent * Ability to complete the Symptom Experience Diary by themselves or with assistance Exclusion Criteria: * Ki-67 of \