ANPEP and neoplasm: As observed in Fig. 1b, flow cytometry data revealed that HT1080 (fibrosarcoma), U-937 (histiocytic lymphoma), and NB-4 (acute promyelocytic leukemia) cells showed high levels of CD13, whereas CD13 expression could not be detected in Raji (Burkitt’s lymphoma), RPMI 8226 (myeloma), and EA.hy926 (endothelium, non-tumor) cells.