ANXA5 and neoplasm: Microscopic analyses also showed specific targeting of PSP1 to apoptotic cancer cells, as was the case for annexin V. Although the affinity of annexin V for PS was significantly (∼103-fold) greater than that of PSP1, our results demonstrated that the same concentration of PSP1 (20 μg/ml) targets apoptotic tumor cells more efficiently than annexin V does.