Decoding the Collagenome in Breast Cancer: Mechanotransduction, Microenvironment, and Translational Opportunities.

Breast cancer (BC) progression is strongly influenced by the extracellular matrix (ECM), whose remodelling regulates tumour growth, invasion, metastasis, immune modulation, and therapeutic response. Among ECM components, collagens have emerged as both structural proteins and active mediators of mechanotransduction, stromal interactions, and tumour cell behaviour. This narrative review analyses collagen families and collagen-associated proteins implicated in BC, integrating evidence on their expression patterns, biological functions, clinical significance, and translational potential. We examine fibrillar and non-fibrillar collagens, including fibril-associated collagens with interrupted triple helices (FACITs), membrane-associated collagens with interrupted triple helices (MACITs), basement membrane (BM) collagens, and multiplexins, together with their interactions with cancer-associated fibroblasts (CAFs), immune cells, and signalling pathways involved in tumour progression. Alterations in collagen composition, organization, crosslinking, and degradation regulate ECM stiffness, epithelial-mesenchymal transition (EMT), invasion, metastatic dissemination, and therapy resistance. Several collagen types and collagen-derived fragments also show promise as prognostic biomarkers and therapeutic targets, particularly in aggressive BC subtypes such as human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancer (TNBC). Overall, this review highlights the collagenome as a dynamic component of the breast tumour microenvironment (TME) and supports collagen-informed strategies for improved patient stratification and targeted therapies.