Updated project metadata. ECM is the physicochemical support for the cells living in the tissue microenvironment. it is important to know the protein contents within the ECM that are critical for extra- and intracellular signaling, cell growth, migration, cell-cell/ECM interactions. The ECM gel derived from the Engelbreth-Holm-Swarm murine sarcoma (commonly known as Matrigel or lrECM) purchased from the Sigma Aldrich in the liquid concentration of 8-12 mg/ml (Lot # 064M4075V) was used for the LC-MS/MS analysis and to prepare the 3D scaffolds used for downstream experiments. The Matrigel mass spectrometry data will be used to compare with those of the decellularized mice mammary tissue ECM/DBT-TMS.