While many of the commonly used chemotherapy agents fit into one of the three previously described groupings (genotoxic, spindle inhibitors, and anti-metabolite), some of them work through mechanisms that do not neatly fit into one of these categories. Additionally, some drugs may not have a clearly defined mechanism of action. Some drugs that fall into these categories:
Arsenic trioxide (Trisenox®)
Bleomycin
Hydroxyurea
Streptozocin