If participant is are enrolled in Phase 1 (Dose De-Escalation), the dose of avelumab participant receives will depend on when participant joins this study. Up to three (3) dose levels of avelumab will be tested. About 3-6 participants will be enrolled at each dose level. The first group of participants will receive the highest dose level of avelumab. If no more than 1 participant has intolerable side effects, up to 3 more participants will be enrolled at that dose level. If no intolerable side effects are seen at that dose level, that is considered the highest tolerated dose. If enough intolerable side effects are seen at the assigned dose level, the total dose of avelumab given in any group may be lowered up to 2 times.