This is a Phase 1b/2, open label, multicenter, safety, clinical activity, pharmacokinetic (PK), and pharmacodynamics (PD) study of avelumab in combination with chemotherapy with or without other anti-cancer immunotherapies, as first-line treatment of adult patients with locally advanced or metastatic solid tumors. Initially, avelumab will be evaluated in combination with pemetrexed and carboplatin in patients with advanced non-squamous non-small cell lung cancer (NSCLC) (Cohort A1) and with gemcitabine and cisplatin in patients with cisplatin-eligible urothelial cancer (UC) (Cohort A2).