Reishi Mushroom Extract for Fatigue and/or Arthralgias/Myalgias in Patients With Breast Cancer on Aromatase Inhibitors

Inclusion Criteria: Age ≥ 18 years History of breast cancer, estrogen receptor positive (ER+), Her 2 positive or negative Fatigue ≥ 4/10 Currently taking any aromatase inhibitor in the curative setting and planning to be on such for at least 8 weeks after registration. (Patients on concurrent ovarian suppression [such as with leuprolide acetate, goserelin] are allowed) Prior treatment: last chemotherapy ≥ 90 days prior to randomization (if treated with chemotherapy) On a stable dose of pain medications if pain medications are being regularly used. (i.e., no change in dosage in the past 30 days) If on supplements, must be on stable dose with no plan to change; not on or planning any acupuncture or other specific supportive modalities for fatigue or AI arthralgias Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0, 1 or 2 White blood cell count (WBC) ≥ 3,000/mm^3 (obtained ≤ 30 days prior to randomization) Hemoglobin ≥ 10 g/dL (obtained ≤ 30 days prior to randomization) Platelet count ≥ 100,000/mm^3 (obtained ≤ 30 days prior to randomization) Total bilirubin ≤ 1.5 x upper limit of normal (ULN) (obtained ≤ 30 days prior to randomization) Alanine aminotransferase (ALT) or aspartate transaminase (AST) ≤ 1.2 x ULN (obtained ≤ 30 days prior to randomization) Prothrombin time (PT)/activated partial thromboplastin time (aPTT) ≤ 1.5 x ULN (obtained ≤ 30 days prior to randomization) Negative pregnancy test done ≤ 7 days prior to registration, for persons of childbearing potential only Provide written informed consent Ability to complete questionnaires Willing to return to enrolling institution during the active monitoring phase of the study Exclusion Criteria: Other known uncontrolled medical conditions causing fatigue such as untreated thyroid disease, depression, fibromyalgia, chronic fatigue syndrome, infection, autoimmune disease, or active/untreated hepatitis Allergy to mushrooms On anticoagulation medication or aspirin or having a known bleeding disorder On any specific medication for fatigue (e.g., methylphenidate) Metastatic cancer diagnosis (history of nodal metastases is allowed) Chronic steroid use, unless on physiologic replacement doses Current use of any medical mushrooms On medications for diabetes History of symptomatic hypotension Taking CYP3A4, CYP2D6 or CYP2E1 substrates Taking CDK4/6 inhibitors or olaparib Any of the following because this study involves an agent that has unknown genotoxic, mutagenic and teratogenic effects: Pregnant persons Nursing persons Persons of childbearing potential who are unwilling to employ adequate contraception