PTN and breast cancer: In the communication between epithelial cells and fibroblasts, the ANGPTL pathway is critical in estrogen receptor-positive breast cancer (ER+BC), while the PTN pathway plays a key role in both ER+BC and human epidermal growth factor receptor 2-positive breast cancer (HER2+BC), and the GAS pathway is associated with poor prognosis in triple-negative breast cancer (TNBC).