Thymidylate synthase (TS) is a substance the body produces naturally. The purpose of this research is to determine if there is a link between TS production and how well patients respond to treatment of non-squamous non-small cell lung cancer (NSCLC). The aim for the future is that doctors could have a better understanding in advance about which patients might respond well to pemetrexed based on how much TS they produce.

All patients on this study will receive 4 intravenous injections of the chemotherapy drugs pemetrexed and cisplatin (with each injection approximately 3 weeks apart). Patients who complete 4 such injections and respond well to their treatment may continue to receive an injection of chemotherapy drug pemetrexed (approximately every 3 weeks). In general terms, treatment will last until either the patient or the doctor decides that there is no clear benefit in continuing with the treatment.

TS levels will be measured from the tumour sample used to make the original diagnosis of NSCLC.

Inclusion Criteria:

• Patients must have Stage 3B or 4 Non-Small Cell Lung Cancer of the non- squamous type
• Patients must at least be able to be physically mobile, take care of yourself and be able to perform light activities such as light housework or office work
• Patients must not have had previous chemotherapy treatment for lung cancer
• Patients must not have had radiotherapy in the last 30 days
• Patients must have measureable tumor lesions according to the Response Evaluation Criteria in Solid Tumors (RECIST) guidelines or disease that can be evaluated on computed tomography (CT) scan
• Patients' test results assessing the function of their blood forming tissue, kidneys, liver and lungs are satisfactory
• Women must be sterile, postmenopausal or on contraception and men must be sterile or on contraception

Exclusion Criteria:

• Patients cannot have received other investigational drugs within the last 30 days
• Patients cannot have any serious, uncontrolled medical condition that might compromise their ability to take part in the study safely
• Patients cannot have a current second primary malignant tumor
• Patients cannot be having current treatment with any other anti-tumor therapy
• Patients cannot have had a yellow fever vaccination within 30 days of enrolment
• Patients who are unable to take vitamins (including injections of vitamin B12) or oral cortisone medication
• Patients who are unable to stop taking more than 1.3 grams of aspirin on a daily basis or non-steroidal anti-inflammatory agents
• Patients who are pregnant or breastfeeding