For example, Richards et al. 21 showed the anticancer effect of the combination of the HDAC inhibitor, CI-994, and gemcitabine in pancreatic cancers; patients receiving CI-994 combined with gemcitabine had a higher incidence of grade 3/4 adverse events such as thrombocytopenia, anemia, and leukopenia than those treated with only gemcitabine. Here, HDAC9 is linked to Decreased total leukocyte count.