Pemetrexed Disodium and Carboplatin in Treating Patients With Extensive-Stage Small Cell Lung Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed small cell lung cancer * Previously untreated disease * No mixed histology * Extensive-stage disease * Clinically significant effusions (e.g., symptomatic pleural effusion) must be drained prior to treatment * Measurable disease, defined as ≥ 1 unidimensionally measurable lesion ≥ 20 mm by conventional techniques OR ≥ 10 mm by spiral CT scan * No symptomatic, untreated, or uncontrolled CNS metastases * CNS metastases previously treated with whole-brain radiotherapy allowed PATIENT CHARACTERISTICS: Age * 18 and over Performance status * ECOG 0-2 Life expectancy * At least 12 weeks Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Hemoglobin ≥ 9.0 g/dL Hepatic * Total bilirubin ≤ 1.5 times upper limit of normal (ULN) OR * Direct bilirubin normal * ALT and AST ≤ 3 times ULN (5 times ULN if there is liver involvement) Renal * Creatinine clearance ≥ 45 mL/min Cardiovascular * No angina pectoris * No congestive heart failure within the past 3 months, unless ejection fraction \> 40% * No cardiac arrhythmia * No myocardial infarction within the past 3 months * No hypertension, including labile hypertension Pulmonary * No interstitial pneumonia * No extensive and symptomatic interstitial fibrosis of the lung Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No history of poor compliance with antihypertensive medication * Able to take folic acid, cyanocobalamin (vitamin B\_12) supplementation, or dexamethasone * No uncontrolled diabetes * No serious condition that would preclude study participation * No clinically significant infection * No significant traumatic injury * No other malignancy within the past 5 years except carcinoma in situ of the cervix or nonmelanoma skin cancer * Low-grade (Gleason score ≤ 6), localized prostate cancer allowed even if diagnosed \< 5 years prior to study entry * No seizure disorder * No other severe and/or uncontrolled medical condition PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent immunotherapy * No concurrent immunomodulating agents Chemotherapy * No other concurrent chemotherapy Endocrine therapy * No concurrent hormonal therapy Radiotherapy * See Disease Characteristics * Prior palliative radiotherapy allowed * No prior palliative radiotherapy to the chest except for ≤ 3 fractions for superior vena cava syndrome * No concurrent radiotherapy Surgery * More than 4 weeks since prior major surgery\* (i.e., laparotomy) or open biopsy * More than 2 weeks since prior minor surgery\* NOTE: \*Insertion of a vascular access device is not considered major or minor surgery Other * More than 4 weeks since prior investigational therapy * No concurrent Hypericum perforatum (St. John's wort) * No concurrent inducers or inhibitors of CYP3A4 * No concurrent medications that are metabolized by CYP3A4 * No aspirin dose ≥ 1.3 grams per day for ≥ 10 days prior to and after study treatment * No other concurrent cytostatic or cytotoxic agents