A Study of BMS-986504 With Standard-of-Care Therapy for People With Solid Tumor Cancer

Inclusion Criteria: * Documentation of Disease: * Patients must have pathologic confirmation of one of three diseases: * Diffuse pleural mesothelioma (DPM) * Gastroesophageal carcinoma (GEC) including adenocarcinoma or squamous cell carcinoma of the esophagus, gastroesophageal junction, or stomach. * PD-L1 CPS ≥1 (using clone 73-10, DAKO) * HER2 overexpression negative (using clone 4B5, Ventana): HER2 IHC 0-1+, or HER2 2+ with ISH showing HER2:CEP17 ratio \<2 and average HER2 copy number \<6.0 signals/cell * Urothelial carcinoma (UC) * Archival tissue is acceptable * Metastatic or advanced/unresectable disease: * For Diffuse Pleural Mesothelioma (DPM) and Gastroesophageal Carcinoma (GEC )cohorts: no prior systemic treatment for metastatic disease * Patients with metastatic disease after treatment for localized GEC may have received prior systemic therapy (chemotherapy and/or chemoradiation) if \>6 months have elapsed between the end of therapy and registration. * One prior cycle of standard-of-care therapy alone without BMS-986504 or other MTAP inhibitors (ipi/nivo for DPM, FOLFOX + nivo for GEC) is acceptable with PI approval. * For UC cohort: must have received at least 1 prior line of treatment without prior gemcitabine (prior tx with Gem+Platinum in the perioperative setting is permitted if at least 12 months have elapsed from trial enrollment) * Patients with recurrent disease within 1 year of completion of prior perioperative systemic therapy are eligible with PI appro…