To investigate immune cell composition and activation during breast cancer onset, MMTV-PyMT mammary glands were dissociated and stained with multiple cell surface markers for flow cytometry quantification using the gating strategy depicted in S2 Fig We compared resident/influxing immune cells, endothelial cells, and epithelial cells in MMTV-PyMT Timp3+/+ and Timp3−⁄− mice during the early window of mammary cancer suppression (day 40). This evidence concerns the gene TIMP3 and breast carcinoma.