The comparative study emphasized that the α-emitting, 213Bi labeled to anti-CD33 monoclonal antibody (mAb) WM53, killed the acute myeloid leukemia (AML) cells through inhibiting DNA synthesis, while the β-emitting, samarium-153 (153Sm), was not effective when using the tritium-labeled thymidine method [65]. Here, CD33 is linked to acute myeloid leukemia.