Apatinib With Pembrolizumab in Previously Treated Advanced Malignancies

Inclusion Criteria: * Male or female subject aged ≥ 18 years. * One of the following advanced solid malignancies which qualifies for standard of care pembrolizumab treatment per FDA approval: * Locally advanced or metastatic urothelial carcinoma that has progressed during or following platinum-based chemotherapy or within 12 months of neoadjuvant/adjuvant platinum-based therapy. Patients may have received any amount of platinum-based therapy. * Unresectable or metastatic MSI-H or dMMR solid tumors that have progressed during or following prior treatment and have no satisfactory alternative treatment options (including MSI-H or dMMR colorectal cancer that has progressed following treatment with a fluoropyrimidine, oxaliplatin, and irinotecan). * Recurrent locally advanced or metastatic, gastric or gastroesophageal junction (GEJ) adenocarcinoma expressing PD-L1 (as determined by an FDA-approved test) that have progressed on or after two or more systemic therapies, including fluoropyrimidine- and platinum-containing chemotherapy and, if appropriate, HER2/neu-targeted therapy. * Patients must have available and be willing to provide formalin fixed paraffin embedded tissue sample from archival tissue (patients who can't provide archival tissue will be offered an optional biopsy; lack of tissue will not be exclusionary). * Have measurable disease based on RECIST 1.1. (For Phase 2 Subjects Only) * Female subject of childbearing potential should have a negative urine or serum…