The article reviews the role of stromal cells and factors in mammary gland development and breast cancer. The mammary gland, which undergoes significant changes throughout the lifetime of reproductive females, displays many properties associated with breast cancer, such as invasion, proliferation, resistance to apoptosis, and angiogenesis. The stroma, comprising adipocytes, fibroblasts, blood vessels, and the extracellular matrix (ECM), plays a crucial role in these processes. Disruption of communication between the epithelium and stroma can induce and promote breast cancer. Key factors and cell types involved in epithelial-stromal crosstalk include TGFβ, Wnt, PTHrP, IGF-I, and inflammatory cells like macrophages and eosinophils. The ECM and stromal factors are essential for proper branching and involution, with excessive side branching leading to tumorigenesis. Understanding these interactions is crucial for developing cures for diseases like breast cancer.The article reviews the role of stromal cells and factors in mammary gland development and breast cancer. The mammary gland, which undergoes significant changes throughout the lifetime of reproductive females, displays many properties associated with breast cancer, such as invasion, proliferation, resistance to apoptosis, and angiogenesis. The stroma, comprising adipocytes, fibroblasts, blood vessels, and the extracellular matrix (ECM), plays a crucial role in these processes. Disruption of communication between the epithelium and stroma can induce and promote breast cancer. Key factors and cell types involved in epithelial-stromal crosstalk include TGFβ, Wnt, PTHrP, IGF-I, and inflammatory cells like macrophages and eosinophils. The ECM and stromal factors are essential for proper branching and involution, with excessive side branching leading to tumorigenesis. Understanding these interactions is crucial for developing cures for diseases like breast cancer.