Updated project metadata. Type I, II, III and V collagens were commonly identified in human, pig, and mouse breast ECM. Mammary epithelial cells were able to form acini on certain types or combinations of the four collagens at normal breast tissue stiffness levels. Comparison of the collagen species in mouse normal breast and breast tumor ECM revealed common and distinct sets of collagens within the two types of tissues. Elevated collagen type I alpha 1 chain expression was found in human breast cancers. Collagen type XXV alpha 1 chain was identified in mouse breast tumors but not in normal breast tissues. Our data provide insights into modeling human breast pathophysiological structures and functions using native tissue-derived hydrogels and potential contributions of different collagen types or their monomers in breast cancer development.