Pemetrexed and Best Supportive Care Versus Placebo and Best Supportive Care in Non-Small Cell Lung Cancer (NSCLC)

Inclusion Criteria:

* Histologic or cytologic diagnosis of NSCLC Stage IIIB (with pleural effusion and/or positive supraclavicular lymph nodes) or Stage IV prior to induction therapy.
* Participants must have had 1 of the following induction therapies for treatment for Stage IIIB (with pleural effusion and/or positive supraclavicular lymph nodes) or IV NSCLC: Gemcitabine plus carboplatin, paclitaxel plus carboplatin, or docetaxel plus carboplatin, gemcitabine plus cisplatin, paclitaxel plus cisplatin or docetaxel plus cisplatin.
* Participants must have received only 1 chemotherapeutic doublet lasting precisely 4 cycles.
* Induction regimens must be based on 21-day cycles.
* Documented evidence of a tumor response of complete response (CR), partial response (PR), or stable disease (SD). Tumor assessment must occur between Cycle 4 (Day 1) of induction therapy and the date of randomization. This response does not have to be confirmed in order for the participant to be randomized. Positron emission tomography (PET) scans and ultrasounds may not be used for lesion measurements for response determination.

Exclusion Criteria:

* With the exception of those chemotherapies listed as inclusion criterion, participants will not be included if they have received prior systemic anticancer therapy (including adjuvant early-stage treatment for NSCLC) or any systemic treatment for any other cancer.
* Have received treatment within the last 30 days with a drug that has not received regulatory approval for any indication at the time of study entry.
* Inability to comply with protocol or study procedures.
* A serious concomitant systemic disorder that would compromise the participant's ability to complete the study.
* A serious cardiac condition, such as myocardial infarction within 6 months, angina, or heart disease, as defined by the New York Heart Association Class III or IV.