This study is a randomized Phase 3, double-blind study of maintenance pemetrexed (Alimta) plus best supportive care versus placebo plus best supportive care in Non Small Cell Lung Cancer (NSCLC). Patients must have received one of six induction regimens for 4 cycles and did not have progressive disease prior to randomization (enrollment) into this trial. It is anticipated that patients that are treated with Alimta plus best supportive care will receive greater anticancer benefit in comparison with those who receive placebo plus best supportive care.

Ages Eligible for Study:  18 Years and above,  Genders Eligible for Study:  Both

Criteria

Inclusion Criteria:

• Diagnosis of NSCLC Stage IIIB (with pleural effusion and/or positive supraclavicular lymph nodes) or Stage IV prior to induction therapy.
• Must receive one of the following induction therapies: Gemcitabine plus carboplatin, paclitaxel plus carboplatin, or docetaxel plus carboplatin.
• Induction regimens must be based on 21-day cycles.
• Prior radiation therapy allowed to <25% of the bone marrow. Prior radiation to the whole pelvis is not allowed.
• Patients must receive on-study therapy no earlier than 21 days and no later than 42 days from their last cycle (Day 1) of induction therapy.

Exclusion Criteria:

• 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 patient's ability to complete the study.
• Inability or unwillingness to take folic acid or vitamin B12.
• Received an induction chemotherapy regimen that was not based on a 21-day cycle.