Pemetrexed in Patients With Advanced Neuroendocrine Tumors

* 1 cycle is equal to 21 days. Every 21 days the following will be performed: a review of the patients symptoms and medications; physical exam; blood tests; vital signs; and pemetrexed infusion. * Every 3 cycles (9 weeks) an assessment of disease extent by CT scan and a 24 hour urine collection (if applicable) will be performed. * Before patients start receiving pemetrexed, they will be given folic acid, vitamin B12 and dexamethasone to help reduce the chance of significant side effects. Dexamethasone will be taken the evening before, the morning before and the evening after receiving pemetrexed. Folic acid should be taken daily beginning 5-7 days before the first dose of pemetrexed and should be continued for three weeks after the last dose of pemetrexed. Vitamin B12 will be given as an injection 1-2 weeks before the first dose of pemetrexed and once every 9 weeks until 3 weeks after the last dose of pemetrexed. * Patients can continue to receive treatment with pemetrexed unless there is evidence that their tumor has grown or they are experiencing serious side effects. * Immediately after the patient has completed the study, they will be given a physical exam, including vital signs, a CT scan, and blood tets. The study staff will continue to monitor the patients health either by clinic visits or phone calls every three months for the remainder of your life.