Feasibility Study of CDDP + CPT-11 + PSK for Extensive-Stage Disease (ED) Small Cell Lung Cancer

Inclusion Criteria: * Patients with histologically or cytologically proven small cell lung cancer * Patients receiving chemotherapy for the first time * Patients with no indication for radical radiotherapy or surgical resection * Patients diagnosed as ED\* by full staging \[chest X ray, chest C, brain CT or MRI, abdominal CT or abdominal ultrasonography, whole body bone scintigraphy (may be replaced by PET/CT)\] * ED: Patient with distant metastasis including contralateral hilar lymph node metastasis, but ipsilateral pleural effusion without distant metastasis is excluded. * Patients with lesions measurable or evaluable by the RECIST criteria * Patients aged from 20 years to below 75 years * Patients with preserved organ functions as indicated by the following test values (data obtained within 14 days prior to registration) Hemoglobin: ≥9.0 g/dL White blood cell count: ≥4,000/mm3, ≤12,000 /mm3 Neutrophil count: ≥ 2,000/mm3 Platelet count: ≥100,000 /mm3 GOT, GPT: below 2.5 times the upper limit of normal range for individual facility Total bilirubin: ≤1.5 mg/dL Serum creatinine: below the lower limit of normal range for individual facility Creatinine clearance: ≥ 60mL/min Arterial oxygen tension （PaO2）: ≥60 torr (resting) * Performance status (PS): 0-1 * Absence of serious concurrent cardiac or pulmonary disease * Patients expected to survive for at least 3 months * Patients from whom written informed consent can be obtained Exclusion Criteria: * Patients with serious infection and other serious complications (including gastrointestinal bleeding and diarrhea) * Patients with pleural effusion, ascites, or pericardial effusion that requires treatments including puncture drainage and intracavity administration * Patients showing definite interstitial pneumonitis or pulmonary fibrosis on plain chest radiograph * Patients manifesting central nervous system symptoms due to brain metastasis at registration * Patients with active multiple cancers * Patients who had undergone bone marrow transplantation * Patients who had undergone peripheral blood stem cell transplantation * Patients with a history of definite drug allergy * Pregnant and nursing patients, patients who may be pregnant or who intend to become pregnant * Male patients with reproductive capacity who have no intention of contraception during the clinical trial * Patients with poorly controlled diabetes * Patients who had been administered Krestin in the past * Others: patients who are judged by the investigator or subinvestigator to be unsuitable as subject