PTEN and breast cancer: Our previous study revealed that daily gentle stretching (~ 25% strain) for 10 min reduced the growth of P53/PTEN - / - orthotopic mouse mammary tumors by 50%.<h4>Results</h4>In this study, we further investigated the mechanism of stretching in a more aggressive MMTV-PYMT (mammary tumor virus- polyomavirus middle T antigen) tumor model in vivo and in vitro and analyzed its impact on collagen reorganization at both the tumor-stromal interface and the tumor microenvironment composition at single-cell level.