Subject Selection A. Inclusion criteria 1. Patients with stage IV HER2+ breast cancer treated to: a. No evidence of disease (NED) , or b. Stable bone only disease after definitive therapy. 2. HER2 overexpression by IHC of 2+ or 3+ in the primary tumor or metastasis; or documented gene amplification by FISH analysis. IHC ≤ 2+ must have HER2 gene amplification documented by FISH. 3. Patients must continue HER2 -targeted monoclonal antibody therapy dosing per standard of care through the entire study period (one year). a. HER2 -targeted monoclonal antibody therapy is defined as either trastuzumab monotherapy, or trastuzumab and pertuzumab combination therapy administered per standard of care. 4. Patients must be at least 21 days post cytotoxic chemotherapy prior to enrollment. 5. Patients must be at least 28 days post immunosuppressants prior to enrollment . 6. Patients must be at least 28 days from use of any mushroom supplements (examples: turkey tail, reishi, maitake, shiitake,) and agree to withhold them for the entire study period (one year). 7. Patients on bisphospho nates and/or endocrine therapy are eligible. 8. Patients who are having sex that could lead to pregnancy must agree to contraceptive use during the entire study period. 9. Patients must have Zubrod Performance Status Score of ≤ 2 (Appendix A). 10. Patients must have recovered from major infections and/or surgical procedures, and in the opinion of the investigator, not have significant active concu rrent medical illnesses precluding study treatment. 11. Laboratory values must be as follows and p erformed within 30 days of enrollment: a. WBC ≥ 3000/mm3 b. Hgb ≥ 10 g/dl c. Serum creatinine ≤ 2.0 mg/dl or creatinine clearance > 60 ml/min d. Total bilirubin ≤ 1.5 mg/dl e. SGOT ≤ 2.5 times the upper limit of normal 12. Patients must be at least 18 years of age 13. Patients must have adequate cardiac function as demonstrated by normal left ventricular ejection fraction (LVEF) ≥ the lower limit of normal for the facility on MUGA scan or echocardiogram (ECHO) within 3 months of enrollment. B. Exclusion criteria 1. Patients with any of the following cardiac conditions: a. Restrictive cardiomyopathy 7866/135 08/23/2021 Page 18 of 39 b. Unstable angina within 6 months prior to enrollment c. New York Heart Association functional class III -IV heart failure d. Symptomatic pericardial effusion. 2. Patients with any contraindication to receiving rhuGM -CSF based products. 3. Patients with any clinically significant autoimmune disease requiring active treatment. 4. Patients receiving any concurrent immunosuppressants . 5. Patients who are pregnant or breast -feeding. 6. Patients who are simultaneously enrolled in other treatment studies . 7. Patients who have received a previous HER2 breast cancer vaccine . 8. Known hypersensitivity reaction to mushroom products . Subjects must meet all of the listed criteria in order to be eligible for study. 7.