This dissertation investigates the role of weaning-induced liver tissue remodeling, known as involution, on stromal cells in the liver. We transcriptionally investigate changes in the liver over the course of a lactation-wean cycle and identify alterations to myeloid cell immune composition. In addition, we investigate the role of hepatic stellate cells, the native liver fibroblasts, and how these cells contribute to postpartum breast cancer liver metastasis.