TAP1 and metastatic neoplasm: Intriguingly, we also found that the TAP-1 deficiency was not regulated by mutations or other defects in the TAP-1 gene in many metastatic tumours, but it was epigenetically regulated (Setiadi et al., 2007b) and could be restored by treatment with HDAC inhibitors, such as trichostatin-A (TSA) (Setiadi et al., 2008a).