RBX7455 Before Surgery for the Treatment of Operable Breast Cancer

PRIMARY OBJECTIVES: I. To determine the safety and tolerability of microbiota-based formulation RBX7455 (RBX7455) given for at least 2 weeks and not more than 4 weeks prior to surgery. II. To evaluate intratumoral immunomodulatory effects, including tumor infiltrating lymphocytes ( TILs), CD4, and CD8 T cells, in operable breast cancer patients. SECONDARY OBJECTIVES: I. To evaluate systemic immunomodulatory effects of RBX7455 by measuring circulating cytokines including IL-1b, IL-2, IL-4, IL-5, IL-6, IL-7, CXCL8 (IL-8), IL-10, IL-12, IL-13, IL- 17A, IFN-gamma, TNF-alpha, CCL2 (MCP-1), CCL4 (MIP-1beta), granulocyte-colony stimulating factor (G-CSF), and granulocyte macrophage (GM)-CSF before and after treatment with RBX7455. II. To assess stool microbiome α-diversity, bacterial abundance, and bacterial taxonomy before and after treatment with RBX7455. III. To assess the durability of bacterial engraftment of RBX7455 in the stool at 8 weeks and 6 months. OUTLINE: Prior to standard of care surgery, patients receive RBX7455 orally (PO) 4 days a week for 2-4 weeks in the absence of disease progression or unacceptable toxicity. After completion of surgery, patients are followed up at 8 weeks and 6 months.