HDAC9 and neoplasm: Vorinostat has been reported to inhibit primarily HDACs 1, 2, 3 and 6,33 which are the ubiquitously expressed HDAC family members that are hypothesized to be responsible for unwanted side effects.10 In contrast, HDAC8 expression has been found to be rather tissue-specific.34 Thus, in terms of unspecific side effects, the targeting of one single enzyme seems to be superior to pan-HDAC inhibition when applied in an appropriate tumor entity that displays oncogenic dependency on that particular HDAC family member.