**8. Conclusions and future perspectives**

There is an impressive number of studies with reference to the antitumor activity of flavonoids. However, even though the metal complexation of flavonoids generally results in enhanced antitumor activity, the number of studies regarding flavonoid metal complexes is much smaller. Moreover, none of the flavonoid metal complexes that have shown great antitumor activity has been included in clinical trials so far. This may happen due to the challenges implied by the study of the multiple possible mechanisms induced by the presence of the metal ion. Stability of the complexes in physiological context may also raise some important issues. Therefore, further studies are required to understand their mechanisms of action and their biotransformation in the human body.
