The expansion of metal-based complexes in the last 20 years has been very intense and many metals have been involved. Among the many compounds studied, the ruthenium-based complex NAMI-A embodies the unique paradigm of the ability to selectively inhibiting and preventing the development and the growth of distant metastases originating from solid tumors in all the tumor models on which it has been tested. An activity that can be detected only in vivo since the compound is virtually free of measurable direct cell cytotoxicity in vitro. Recently, a published paper reported on a significant in vitro cytotoxicity against some leukemic cells. The present study was undertaken to reproduce those experiments to further support this novel antileukemic activity that would have put NAMI-A on a new trajectory for development. Our results do not confirm the efficacy of NAMI-A in vitro against the human HL-60 promyelocytic leukemia cell line either using test cultures identical to those reported in the study of reference or in even more stressed conditions, supporting the lack of in vitro direct cell cytotoxicity of NAMI-A. The present study also helps to elucidate that many factors can influence the outcome of in vitro tests of cytotoxicity and suggests caution to speculate on possible therapeutic properties based on the results of simple and reductive in vitro tests of cytotoxicity.