After more than 5 years in the top spot, Epizyme ($EPZM) CEO Robert Gould is stepping down next month, leaving the company as it presses forward with a pair of promising cancer drugs. Gould will leave the post Sept. 10, maintaining a seat on the board as he is replaced by Robert Bazemore, who served as chief operating officer of Synageva until Alexion Pharmaceuticals ($ALXN) bought it for $8.4 billion last month. Meanwhile, Epizyme is advancing two treatments for blood cancers, hoping to replicate positive Phase I results in mid-stage trials. Release