Inclusion Criteria - Pre-Registration:

• Age ≥ 18 years.
• Histological confirmation of HER2 positive breast cancer stage I-III per AJCC staging 8th edition.
• Provide written informed consent.
• Breast cancer patients who will be receiving pertuzumab-based chemotherapy with either TCHP (docetaxel, carboplatin, trastuzumab, and pertuzumab) or docetaxel/paclitaxel, trastuzumab, and pertuzumab.
• ECOG Performance Status (PS) 0, 1, or 2.
• The following laboratory values obtained ≤ 30 days prior to pre-registration:
  • Hemoglobin ≥ 10.0 g/dL;
  • Absolute neutrophil count (ANC) ≥ 1.5 x 10^9/L;
  • Platelet count ≥ 100 x 109/L;
  • Total Bilirubin ≤ 1.5 x ULN (institutional upper limit of normal);
  • AST (SGOT)/ALT (SGPT) ≤ 2.5 x ULN;
  • Serum or plasma creatinine ≤ 1.5 x ULN;
  • Calculated creatinine clearance ≥ 45 ml/min using the Cockcroft-Gault formula below:

    Cockcroft-Gault Equation:

    Creatinine clearance for males = (140 - age)(weight in kg)(72)(serum creatinine in mg/dL)

    Creatinine clearance for females = (140 - age)(weight in kg)(0.85)(72)(serum creatinine in mg/dL).

• Negative serum pregnancy test done ≤30 days prior to pre-registration, for person of childbearing potential only.
• Willingness to return to enrolling institution for follow-up (during the Active Monitoring Phase of the study).
• Willingness to provide mandatory stool  specimen for correlative research.
• Ability to complete questionnaire(s) by themselves or with assistance.

Inclusion Criteria - Registration:

• Received pertuzumab based regimens in the adjuvant or neoadjuvant setting.
• The following laboratory values obtained ≤ 14 days prior to registration:
  • Hemoglobin ≥ 8.0 g/dL;
  • Absolute neutrophil count (ANC) ≥ 1.5 x 10^9/L;
  • Platelet count ≥ 100 x 10^9/L;
  • Total Bilirubin ≤ 1.5 x ULN (institutional upper limit of normal);
  • AST (SGOT)/ALT (SGPT) ≤ 2.5 x ULN;
  • Serum or plasma creatinine ≤ 1.5 x ULN
  • Calculated creatinine clearance ≥ 45 ml/min using the Cockcroft-Gault formula below:

  • Cockcroft-Gault Equation:

    Creatinine clearance for males = (140 - age)(weight in kg)(72)(serum creatinine in mg/dL);

    Creatinine clearance for females = (140 - age)(weight in kg)(0.85)(72)(serum creatinine in mg/dL).

Exclusion Criteria - Pre-Registration:

• History of myocardial infarction ≤ 6 months prior to pre-registration, or congestive heart failure requiring use of ongoing maintenance therapy for life-threatening ventricular arrhythmias.
• Failure to recover from acute, reversible effects of prior therapy regardless of interval since last treatment.
  • EXCEPTION: Grade 1 peripheral (sensory) neuropathy that has been stable for at least 3 months since completion of prior treatment
• Uncontrolled intercurrent non-cardiac illness including, but not limited to:
  • Ongoing or active infection;
  • Psychiatric illness/social situations; 
  • Dyspnea at rest due to complications of advanced malignancy or other disease that requires continuous oxygen therapy;
  • Any other conditions that would limit compliance with study requirements.
• Immunocompromised patients and patients known to be human immunodeficiency virus (HIV) positive and currently receiving antiretroviral therapy. 
  • NOTE: Patients known to be HIV positive, but without clinical evidence of an immunocompromised state, are eligible for this trial.
• Receiving any other investigational agent which would be considered as a treatment for the primary neoplasm (adjust to protocol if applicable).
• Any of the following because this study involves an agent whose genotoxic, mutagenic and teratogenic effects on the developing fetus and newborn are unknown:
  • Pregnant women;
  • Nursing women;
  • Women of childbearing potential who are unwilling to employ adequate contraception.
• Current colostomy or ileostomy.
• History of inflammatory bowel disease.
• History of irritable bowel syndrome.
• History of arteriovenous malformations.
• History of gastrointestinal bleeds.
• Previous surgical resection of the small bowel or colon.
• Previous allergy to rifaximin or its derivatives.

Eligibility last updated 8/19/21. Questions regarding updates should be directed to the study team contact.