Bestatin, due to its competitive, reversible protease inhibitor properties, has an antiangiogenic effect through the inhibition of APN/CD13's activity in numerous tumors (e.g., murine colon adenocarcinoma and myeloid leukemia [33], human promyelocytic leukemia [34], human choriocarcinoma [35], murine melanoma [36, 37], murine lung carcinoma [37], human prostate cancer [38], and human fibrosarcoma [39]). Here, ANPEP is linked to acute promyelocytic leukemia.