To determine the most critical one(s) among them, we tested the inhibitory effects of the pan-HDAC inhibitor panobinostat, the HDAC6-specific inhibitor tubastatin A, and the proteasome inhibitor bortezomib, which exerts anti-tumor effects on teratoma formation via the down-regulation of class I HDACs [14, 15]. This evidence concerns the gene HDAC9 and teratoma.