PECAM1 and neoplasm: Attributing increased migration through stromal cells to the decrease in a subpopulation that expresses CD31 or the amount of CD31-receptors on this subpopulation identifies a unifying mechanism for enhanced tumor migration not only in the mice, but also in patients with breast and prostate cancer, in whom the presence of tumor cells in the bone marrow was associated with diminished CD31 expression [13].