Cyclophosphamide for Nasopharyngeal Carcinoma

Inclusion Criteria:

* Inoperable locoregionally advanced recurrent NPC of undifferentiated type beyond curative surgical resection or second and subsequent courses of radical radiotherapy or metastatic disease who all had received at least 2 lines palliative systemic chemotherapy
* Adequate hematological function defined as absolute neutrophil count ≥1.5 × 10\^9/l; hemoglobin ≥9.0 g/dl and platelet ≥100 × 10\^9/l
* Adequate renal function defined as serum creatinine ≤1.5 × upper normal limit
* Adequate hepatic function defined as serum bilirubin ≤1.5 × upper normal limit; alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤3 × upper normal limit for patients without liver metastases or ≤5 × upper normal limit for those with liver metastases
* Measurable disease according to the RECIST criteria (version 1.1), for the evaluation of measurable disease

Exclusion Criteria:

* Eastern Cooperative Oncology Group (ECOG) performance status 3 or above
* Known brain metastases or leptomeningeal metastases; Note: symptomatic, and/or if they require immunosuppressive doses of corticosteroids (e.g. \> 10 mg/day prednisone or equivalents) for at least 2 weeks prior to study drug administration; patients with treated brain metastases who are deemed clinically stable and without radiological progression on positron emission tomography (PET), MRI or computed tomography (CT) scan performed =\< 8 weeks of study entry, are not excluded; Note: primary nasopharyngeal cancers that directly invade the skull base and extend into the infratemporal fossa (e) are not regarded as brain metastases and are not excluded
* History of allergic reactions attributed to compounds of similar chemical or biologic composition to cyclophosphamide
* History of severe hypersensitivity reaction to any monoclonal antibody
* Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
* Any of the following:
* Pregnant women
* Nursing women
* Men or women of childbearing potential who are unwilling to employ adequate contraception Note: breastfeeding should be discontinued if the mother is treated with cyclophosphamide; women of childbearing potential and men must use two forms of contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation; they must adhere to contraception for a period of 31 weeks after the last dose of cyclophosphamide
* For patients with unknown human immunodeficiency virus (HIV) status at the time of enrollment, HIV serology must be tested during screening; patients who are tested positive for HIV could be included if there is an adequate cluster of differentiation 4 (CD4) count (\> 350/ul) on a stable regimen of highly active anti-retroviral therapy (HAART) with no detectable or minimal viral burden, and no active infections
* Those who cannot provide written informed consent