Vaccine Therapy With or Without Polysaccharide-K in Treating Patients With Stage IV HER2 Positive Breast Cancer Receiving HER2-Targeted Monoclonal Antibody Therapy

Inclusion Criteria:

Patients with stage IV HER2+ breast cancer treated to:

No evidence of disease (NED), or
Stable bone only disease after definitive therapy
HER2 overexpression by immunohistochemistry (IHC) of 2+ or 3+ in the primary tumor or metastasis; or documented gene amplification by fluorescent in situ hybridization (FISH) analysis; IHC =< 2+ must have HER2 gene amplification documented by FISH

Patients must continue HER2-targeted monoclonal antibody therapy dosing per standard of care through the entire study period (one year)

HER2-targeted monoclonal antibody therapy is defined as either trastuzumab monotherapy, or trastuzumab and pertuzumab combination therapy administered per standard of care
Patients must be at least 21 days post cytotoxic chemotherapy prior to enrollment
Patients must be at least 28 days post immunosuppressants prior to enrollment
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)
Patients on bisphosphonates and/or endocrine therapy are eligible
Patients who are having sex that could lead to pregnancy must agree to contraceptive use during the entire study period
Patients must have Zubrod performance status score of =< 2
Patients must have recovered from major infections and/or surgical procedures, and in the opinion of the investigator, not have significant active concurrent medical illnesses precluding study treatment
White blood cell (WBC) >= 3000/mm^3
Hemoglobin (Hgb) >= 10 g/dl
Serum creatinine =< 2.0 mg/dl or creatinine clearance > 60 ml/min
Total bilirubin =< 1.5 mg/dl
Serum glutamic oxaloacetic transaminase (SGOT) =< 2.5 times the upper limit of normal
Patients must have adequate cardiac function as demonstrated by normal left ventricular ejection fraction (LVEF) >= the lower limit of normal for the facility on multi gated acquisition (MUGA) scan or echocardiogram (ECHO) within 3 months of enrollment

Exclusion Criteria:

Patients with any of the following cardiac conditions:

Restrictive cardiomyopathy
Unstable angina within 6 months prior to enrollment
New York Heart Association functional class III-IV heart failure
Symptomatic pericardial effusion
Patients with any contraindication to receiving rhu granulocyte macrophage colony stimulating factor (rhuGM-CSF) based products
Patients with any clinically significant autoimmune disease requiring active treatment
Patients receiving any concurrent immunosuppressants
Patients who are pregnant or breast-feeding
Patients who are simultaneously enrolled in other treatment studies
Patients who have received a previous HER2 breast cancer vaccine
Known hypersensitivity reaction to mushroom products