Eligible patients with biopsiable (biopsied) disease will receive nivolumab 240 mg IV every 2 weeks x 6 doses then 360 mg every 3 weeks for up to 84 weeks. Tumor response will be assessed at weeks 12, 18 and 24 and then every 12 weeks. For patients who experience RECIST 1.1 defined PD, but remain clinically stable (and asymptomatic), a confirmatory scan after 6 weeks (± 1 week) of additional therapy is suggested. Patients with persistent PD at confirmatory scan will be evaluated for enrollment on Part B of this study. Symptomatic patients may be evaluated for Part B immediately. Patients without confirmed PD can continue on nivolumab therapy.