HDAC9 and neoplasm: High expression levels of class I HDACs correlated with tumour dedifferentiation and higher proliferative fractions (measures by Ki-67) in prostate carcinoma, which is in line with in vitro studies, which showed that high HDAC activity leads to tumour dedifferentiation and enhanced tumour cell proliferation (Munster et al, 2001; Floryk and Huberman, 2005; Uchida et al, 2005).