Pemetrexed Disodium/Observation in Treating Patients W/ Malignant Pleural Mesothelioma w/Out Progressive Disease After 1st Line Chemotherapy

Inclusion Criteria: * Histologically confirmed malignant pleural mesothelioma meeting 1 of the following cell types: * Epithelial * Sarcomatoid * Mixed type * Histologically documented malignant pleural mesothelioma, epithelial, sarcomatoid or mixed type, not amenable to surgical resection * Prior treatment * Currently receiving first-line treatment with pemetrexed + platinum; patients are to be registered to Cancer and Leukemia Group B (CALGB) 30901 no later than the last day of cycle 4 of first line therapy * Prior intracavitary cytotoxic or sclerosing therapy (including bleomycin) are acceptable; prior intrapleural cytotoxic chemotherapy will not be considered systemic chemotherapy * Prior surgical treatment is allowed * Prior radiation therapy is allowed * Non-pregnant and non-nursing; women of child bearing potential and men must agree to use an appropriate method of birth control throughout their participation in this study; appropriate methods of birth control include abstinence, oral contraceptives, implantable hormonal contraceptives (Norplant), or double barrier methods (diaphragm plus condom) * RANDOMIZATION ELIGIBILITY CRITERIA * Patients with complete response, partial response, or stable disease following 4, 5 or 6 cycles of first-line chemotherapy with pemetrexed AND either cisplatin or carboplatin; a maximum of 6 cycles of chemotherapy may have been given * Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 * Granul…