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 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 par…