More than 350 clinical trials have been completed or are underway using HDAC inhibitors, both as single agents or in combination, for the treatment of malignancies, including haematological malignancies.123, 124 The most successful combination therapy is the rationally designed combination of HDAC inhibition and proteasome inhibition.125 Two phase II clinical trials have been conducted with vorinostat and bortezomib for relapsing or refractory multiple myeloma with a response rate of 42 and 27%, respectively.126, 127 Another combination of vorinostat and marizomib in patients with melanoma. Here, HDAC9 is linked to melanoma.