Support Theaters in America Growth and Expansion Act or the STAGE Act - Amends the Internal Revenue Code, with respect to the expensing of the costs of qualified film and television productions, to: (1) extend through 2015 provisions allowing such expensing, (2) allow such expensing for the costs of certain live theatrical productions, and (3) provide for the tax treatment of dispositions of an interest in a live theatrical production as a passive activity.