Breast cancer is a heterogeneous, multi-factorial disease of aberrant breast development whose etiology relies upon several microenvironmental changes within the tissue. Within the last decade, it has become widely accepted that tumor cells frequently rely on signals from an activated microenvironment in order to proliferate and survive within a tissue. This activated tissue microenvironment involves the appearance of αSMA + fibroblasts (referred to as "cancer associated fibroblasts"), the recruitment of various immune cells (macrophages, T cells, B cells, T regulatory cells), enhanced collagen I deposition, and epigenetic modifications of stromal cells. These stromal changes can predict patient survival and correlate with distinct breast tumor subtypes. Characterizing these stromal changes will facilitate their use as clinical biomarkers in breast cancer, and may facilitate their use as potential drug targets for adjuvant breast cancer therapy.