Perlmutter Cancer Center

This is a phase II, unblended, single arm study where 48 evaluable subjects will be enrolled. Each subject will participate in the trial from the time the subject signs the Informed Consent Form (ICF) through the final protocol-specified evaluation. Each patient will undergo screening and then be treated with reirradiation with 1.2 Gy BID, 5 days a week (weeks 1-5). MK-3475 will be given at 200mg intravenous every 3 weeks starting day one of reirradiation and will be continued in all patients until 3 months post completion of reirradiation, at which time a PET/CT will be done to evaluate response. Patients with progressive disease (PD) will be taken off the study. Patients that have a complete response (CR) will be followed clinically and radiographically, and if disease recurs may be eligible to be retreated with MK-3475 for up to one year. Patients with partial response (PR) or stable disease (SD) will continue treatment with MK-3475 for up to two years unless one of the following occurs: --documented disease progression --unacceptable adverse event(s) --intercurrent illness that prevents further administration of treatment --investigator decision to withdraw the subject --subject withdraw of consent --subject pregnancy --subject noncompliance --administrative reasons (i.e. trial is closed prematurely). Patients who have not progressed at completion of 24 months of therapy will be observed, but may be eligible for 1 year of retreatment with MK- 3475 if they develop recurrence/progression if they qualify as detailed in the protocol and if the trial is still ongoing.