UPP1 and breast cancer: However, the proportion of MMTV-PyMT mice that had lung metastases at clinical endpoint was significantly reduced, from 85% in Upp1+/+ mice to 52% in Upp1−/− mice (Figs. 6B and EV6B–D), indicating that the role of UPP1 in mammary cancer is specific to the metastatic process (Fig. 6C).