Reishi Mushroom Extract for Fatigue And/or Arthralgias/myalgias in Patients with Breast Cancer on Aromatase Inhibitors

Eligibility Criteria

• * Age ≥ 18 years
• * History of breast cancer, estrogen receptor positive (ER+), Her 2 positive or negative
• * Fatigue ≥ 4/10
• * Currently post-menopausal (as defined by National Comprehensive Cancer Network (version 4.2024), 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) ; CDK 4/6 inhibitors abemaciclib, ribociclib 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 on concurrent ovarian suppression only
• * Provide informed consent
• * Ability to complete questionnaires
• * Willing to return to enrolling institution during the active monitoring phase of the study
• * 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 sensitive substrates which can be located at the following link:
• * Drugs which exhibit either \>20% inhibition or \>20% induction of CYP2E1 in vivo, such as: Acetaminophen, Dapsone, Enflurane, Halothane, Isoflurane, \& Theophylline
• * Taking olaparib
• * Any of the following because this study involves an agent that has unknown genotoxic, mutagenic and teratogenic effects:
• * Pregnant persons
• * Nursing persons
• * Persons on concurrent ovarian suppression who are unwilling to employ adequate contraception (e.g., hormonal methods, barrier methods, intrauterine device, abstinence)