If enrolled in the study, you will receive intravenous (in the vein) infusions of demcizumab (or placebo), carboplatin, and pemetrexed administered on the same day, every 21 days for 4 cycles, or until it has been shown that your cancer has gotten worse. If your physician decides to delay treatment with one of the agents due to side effects, the other agents may still be administered as scheduled. After 4 cycles, if you have stable or improved disease, you will continue to receive pemetrexed once every 21 days as maintenance therapy. After 8 cycles, if you have stable or improved disease, you may receive demcizumab (or placebo), every 21 days for 4 more cycles.