Clonal hematopoiesis describes a common pre-cancerous condition where blood stem cells gain mutations in cancer-associated genes that allow them to grow and expand abnormally. This condition occurs more frequently with increasing age and after chemotherapy for solid tumors where it is a strong risk factor for developing secondary blood cancers. Inflammation after chemotherapy exposure is known to favor proliferation of mutant blood stem cells. We are investigating the anti-inflammatory effects of metformin on mutant blood stem cell behavior and how the presence of clonal hematopoiesis impacts clinical outcomes in women who received curative-intent chemotherapy after surgery for advanced breast cancer.