Inclusion Criteria:

- Histologically or cytologically confirmed neuroendocrine tumors

- Progressive and measurable metastatic disease

- Patients must not have disease that is currently amenable to surgery

- Life expectancy of greater than 3 months

- ECOG performance status ≤2

- Patients must have normal organ and marrow function

- Negative pregnancy test; agreement to use adequate birth control

Exclusion Criteria:

- Patients receiving chemotherapy or radiotherapy within last 4 weeks

- Patients that had received Sorafenib for advanced NET(neuroendocrine tumors) are
not allowed

- Any other investigational agents within 4 weeks of study

- Patients with known brain metastases

- History of allergic reactions to compounds of similar chemical/biologic composition
to sorafenib or cyclophosphamide

- Concurrent cancer from another primary site requiring treatment within the past 3
years

- Uncontrolled intercurrent illness

- Pregnant women and women who are breastfeeding

- HIV-positive patients receiving combination anti-retroviral therapy