Single Agent Alimta in Poor Performance Status in Non-small Cell Lung Cancer

Inclusion Criteria: 1. Histologically or cytologically proven Stage IIIB (T4 lesion due to malignant pleural or pericardial effusion) or Stage IV. Clinically significant pleural or peritoneal effusions should be drained prior to dosing. 2. Zubrod PS 2 or PS 3 3. Patients with asymptomatic brain metastases and no requirement for corticosteroids or anticonvulsants are eligible for this clinical trial. 4. Measurable OR non-measurable disease documented by CT or MRI. 5. Patients may have had \</=1 prior chemotherapy regimens but multiple prior biologic regimens. At least 4 weeks need to have elapsed since last chemotherapy or biologic therapy administration. 6. Prior radiation therapy is permitted; however, at least two weeks must have elapsed since the completion of prior radiation therapy and patients must have recovered from all associated toxicities at the time of registration. Measurable or non-measurable disease must be outside the previous radiation field OR patients with visible progression or new lesions within the radiation field are eligible. 7. At least two weeks must have elapsed since surgery and patients must have recovered from all associated toxicities at the time of registration. 8. Creatinine clearance \>/= 45 cc/min measured or calculated using the following formula: Calculated Creatinine Clearance = (140 - age) X WT (kg) X (0.85 if female)/72 X creatinine (mg/dl) Calculated Creatinine Clearance = (140 - age) X WT (kg) X (1.00 if male)/72 X creatinine (mg/dl) 9. Absolute neutrophil count (ANC) \>/= 1,500/µl 10. Platelet \>/= 100,000/µl 11. ALT/AST: \</=3.0 x upper limit of normal (ULN) except in known hepatic metastasis wherein may be \</= 5 x ULN 12. Bilirubin: \</=1.5 x ULN 13. Hemoglobin: \>/=9.0 x 10\^9/L 14. Patient must not be pregnant or breastfeeding. Patients of childbearing potential agree to practice an effective contraceptive method for the duration of the study. 15. Patients must be informed of the investigational nature of this study and must sign and give written informed consent in accordance with institutional and federal guidelines. 16. Men and women, aged \>/=18 years. Exclusion Criteria: 1. Prior treatment with pemetrexed therapy. 2. Patients planning to receive any other concomitant anticancer treatment including chemotherapy, radiation therapy, biologic agents or any other investigational drugs. 3. Women who are pregnant or breastfeeding may not participate in this trial. All women of childbearing potential must have a negative pregnancy test within 24 hours prior to enrolling in the study. 4. Inability to interrupt aspirin or other nonsteroidal anti-inflammatory agents for a 5-day period (8-day period for long-acting agents, such as piroxicam). 5. Inability and unwillingness to take folic acid or vitamin B12 supplementation. 6. Inability to take corticosteroids. 7. Prior malignancy except for the following: adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, adequately treated Stage I or II cancer from which the patient is currently in complete remission or other cancer from which the patient has been disease-free for \>/= 5 years.