HDAC9 and Miyoshi myopathy: This review focuses on molecularly targeted therapies that are currently evaluated in clinical trials in the treatment of relapsed/refractory MM patients, which are based on unique cell signaling pathways activated in MM and not in normal cells, including inhibitors of HDAC, PI3K/AKT/mTOR, p38 MAPK, Hsp90, Wnt, Notch, Hedgehog, and cell cycle.