RBX7455 Before Surgery for the Treatment of Operable Breast Cancer

Inclusion Criteria:

Eastern Cooperative Oncology Group (ECOG) performance status =< 2

Histologically confirmed un-resected operable invasive adenocarcinoma of the breast >= 0.5cm

For cohort 1: Estrogen receptor (ER) and/or progesterone receptor (PR) positive >= 10%, and no human epidermal growth factor receptor 2 (HER2) amplification or overexpression
For cohort 2: Human epidermal growth factor receptor 2 (HER2) amplification with fluorescence in situ hybridization (FISH) ratio >= 2.0 or overexpression by immunohistochemistry 3+ with any ER and/or PR
For cohort 3: Triple negative. Estrogen receptor (ER) and/or progesterone receptor (PR) negative < 10%, and no human epidermal growth factor receptor 2 (HER2) amplification or overexpression
Patients must not receive neoadjuvant chemotherapy prior to surgery
Absolute neutrophil count (ANC) >= 1000/mm^3
Platelet count >= 75,000/mm^3
Hemoglobin >= 9.0 g/dL
Creatinine =< 2 x upper limit of normal (ULN)
Serum glutamic-oxaloacetic transaminase (SGOT) (aspartate aminotransferase [AST]) =< 2 x ULN
Albumin >= 3 g/dL
Willing and able to swallow capsules
Willing and able to complete the stool and serum testing required for the study
Willing to provide blood samples for correlative research purposes
Agrees not to take non-dietary probiotics through 8 weeks after receiving the course of study drug (including over-the counter [OTC] and prescription)
Agrees not to take any oral vancomycin, metronidazole, fidaxomicin, rifaximin, nitazoxanide, bezlotoxumab and intravenous immunoglobulin therapy (IVIG) through the 8-week follow-up assessment unless newly prescribed by a treating investigator during the course of the study

Willing to employ adequate contraception from the time of enrollment through 3 months after the final dose of RBX7455

Note: Adequate contraception methods include birth control pills, barrier device, intrauterine device
Capable of understanding the investigative nature, potential risks, and benefits of the study
Capable of providing valid informed consent
Willing to return to enrolling institution for all study visits (blood draws, etc)
Willing and able to complete the required Patient Medication Diary
Willing and able to meet all study requirements, including attending all assessment visits and telephone calls
Women of child bearing potential must have negative pregnancy test within 7 days of enrollment

Exclusion Criteria:

Requires systemic antibiotic therapy for other condition
Fecal microbiota transplant (FMT) within the past 6 months
FMT with an associated serious adverse event related to the FMT product or procedure
Co-morbid systemic illnesses or other severe concurrent disease which, in the judgment of the investigator, would make the patient inappropriate for entry into this study or interfere significantly with the proper assessment of safety and toxicity of the prescribed regimen

Immunocompromised patients including patients known to be human immunodeficiency virus (HIV) positive or those on chronic steroids > 20 mg prednisone a day or prednisone-equivalent

Note: Must be off systemic steroids at least 90 days prior to enrollment. However, topical steroids, inhalants or steroid eye drops are permitted
Receiving any other investigational agent
History of inflammatory bowel disease (IBD), e.g., ulcerative colitis, Crohn's disease, or microscopic colitis
Diagnosis of irritable bowel syndrome (IBS) as determined by Rome III criteria
History of chronic diarrhea
History of celiac disease
Currently has a colostomy
Intraabdominal surgery related to gastrointestinal tract within the last 60 days
Evidence of active, severe colitis
History of short gut syndrome or motility disorders
Requires the regular use of medications to manage bowel hypermotility
Active autoimmune disease that has required systemic treatment in the =< 30 days (i.e., with use of disease modifying agents, corticosteroids, or immunosuppressive drugs) prior to randomization. Note: Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency) is not considered a form of systemic treatment. Patients with vitiligo, Graves' disease, or psoriasis not requiring systemic treatment within the past 30 days are not excluded
Pregnancy
Breast feeding