A review. The promising drug candidate indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019) is the second Ru-based anticancer agent to enter clin. trials. In this review, which is an update of a paper from 2006, the exptl. evidence for the proposed mode of action of this coordination compd. is discussed, including transport into the cell via the transferrin cycle and activation by redn. The results of the early clin. development of KP1019 are summarized in which 5 out of 6 evaluated patients experienced disease stabilization with no severe side effects.