Functional Imaging of T-Cell Activation With [18F]F-AraG in Urothelial Carcinoma Patients Receiving Neoadjuvant Therapy or Patients With Cancer Receiving Standard of Care Anti-PD-1/L1

Inclusion Criteria: * Histologically or cytologically documented cancer to which anti-PD1 or anti-PDL1 are approved therapies * Eligible for with plan to undergo neoadjuvant treatment with atezolizumab followed by surgery as part of a companion study (NCT02451423), or planned to undergo treatment with anti-PD-1 or anti-PD-L1 per standard of care * Must have measurable disease by Response Evaluation Criteria in Solid Tumors (RECIST) version (v)1.1 regardless of disease stage (e.g. localized, locally advanced, or metastatic) * In female patients, negative pregnancy test with no plans to become pregnant during the duration of the study * Able to provide informed consent and follow the study guidelines * Archival tumor tissue from biopsy or resection will be required for all patients; archival tissue should be of good quality based on total and viable tumor contents; fine needle aspiration, brushing, and cytologic cell pellets are not acceptable Exclusion Criteria: * History of prior treatment with immune checkpoint antibodies (e.g. anti-PD1, anti-PDL1, anti-CTLA4 antibody) or co-stimulatory agonist antibodies (e.g. anti-41BB, anti-OX40) \* Prior intravesical treatment with Bacillus Calmette-Guerin (BCG) is allowed; however, the last dose must be at least 6 weeks from time of enrollment and patients must have documented progressive disease at least 6 weeks from completion of last BCG * Diagnosis of immunodeficiency including history of human immunodeficiency virus (HIV) * Receiving systemic steroid therapy or any form of immunosuppressive therapy within 7 days prior to first injection of \[18F\]F-AraG \* Topical and inhaled corticosteroids are allowed * Prior allogeneic stem cell or solid organ transplant * Known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the study * Biopsy or resection of the primary tumor within 14 days the first injection of \[18F\]F-AraG * Contraindication to magnetic resonance (MRI) imaging, as determined through review of the University of California, San Francisco (UCSF) MRI screening form by study investigator * Evidence of active infection within 14 days of study enrollment * Female patients who are pregnant or breastfeeding * Inability to receive furosemide (Lasix) in the opinion of the treating investigator * Patients that plan to receive off-label use of anti-PD1 or anti-PDL1