 - Had prior treatment targeting PD-1:PD-L1 axis or cytotoxic T-lymphocyte-associated protein CTLA, or was previously randomized in any pembrolizumab study. Examples of such agents include but are not limited to: Nivolumab BMS-936558, MDX-1106 or ONO-4538; Pidilizumab CT-011; AMP-224; BMS-936559 MDX-1105; MPDL3280A RG7446; and MEDI4736. 