- Patients must have available and be willing to submit a minimum of five unstained slides from primary, lymph node, or metastatic site to determine PD-L1 expression; the tumor tissue must be adequate for PD-L1 testing (defined as >= 100 tumor cells as confirmed by the treating institution's local pathologist); this must be documented by having a pathologist sign the S1404 Local Pathology Review form prior to step 1 registration; the specimens may come from an archived block but must be submitted within 20 days from cutting the slides