4. Previous treatment with a PD-1 or PD-L1 inhibitor with documented progression of disease on most recent CT scan. Progression of disease is defined as 1) the appearance of a new measureable lesion (>10 mm) on cross-sectional imaging or physical examination OR 2) enlargement of previously detected lesions on two consecutive imaging studies OR 3) enlargement of a previously detected lesion with correlative symptomatology on one cross-sectional imaging study. Patients remain eligible if they had a previous response to a PD-1 inhibitor, including patients who had a complete response, partial response or stable disease (SD). Primary progressing patients are defined as those who received anti-PD-1 therapy within 2 months of study enrollment. Patients with relapsed disease are defined as those who received their last dose of PD-1 blocking antibody ≥2 months prior to enrollment.