PECAM1 and neoplasm: Both the newly identified CD31+ integrin β1+ Sca1- population and the previously identified population of the non-hematopoietic CD31+Sca-1+CD146+CD44- bone marrow cells correlated with tumor cell homing in the same mice in the PTH/ZA model, while in the other four models the previously identified subpopulation did not show any relationship to tumor cell numbers (Fig. 5e-f and Supplementary Fig. 9) [13].