A Phase 1 Study of the Safety and Tolerability of CTX-10726

Inclusion Criteria: 1. Age 18 years or older. 2. Patients must have a histologically or cytologically confirmed diagnosis of locally advanced unresectable or metastatic disease that is relapsed/refractory to standard therapy or for which no effective standard therapy is available, including: 2a: Renal Cell Carcinoma (RCC) * Histologically confirmed diagnosis of renal cell carcinoma (with clear cell component) with advanced or metastatic disease that is not amenable to cure by surgery or other means. * Patients who have progressed after a minimum of 2 doses of a programmed cell death 1 (PD-1)/ programmed cell death ligand 1 (PDL1) treatment. * Patients must have received at least one regimen including a tyrosine kinase inhibitor (TKI). * Patients who received immunomodulatory drugs (thymosin, interferon, interleukin, etc.) within 2 weeks before the first dose or received major surgical treatment within 3 weeks before the first dose are not eligible. 2b: Hepatocellular Carcinoma (HCC) * Patients who have progressed after a minimum of 2 doses of a PD-1/PDL1 treatment. * Patient must have received one of the following regimens: ipilimumab+nivolumab, tremelimumab+durvalumab, atezolizumab+bevacizumab or lenvatinib+pembrolizumab. * Hepatic function: Child -Pugh A and Child-Pugh B7. * Receipt of local area treatment of the liver more than 4 weeks prior to the first dose is allowed. 2c. Gastroesophageal Cancer (GC) * Patients who have progressed after a minimum of 2 doses of a PD-1/PDL1 treatment. * Patients must have received prior treatment with platinum-based chemotherapy. 2d: Endometrial Cancer (EC) * Patients must have received at least 1 cycle of platinum-based chemotherapy. * Patients with newly diagnosed advanced endometrial cancer that have persistent lesion(s) after standard treatment with surgery and chemotherapy ± radiotherapy. * Patients with MSI- high or deficient DNA mismatch repair (dMMR) tumors who have progressed after a minimum of 2 doses of a PD-1/PDL1 treatment. 3\. Patients must have measurable disease per RECIST 1.1. Tumor sites that are considered measurable must not have received prior radiation. 4\. Eastern Cooperative Oncology Group (ECOG) performance status 0-1. 5\. Adequate organ function including: * Bone marrow function defined by absolute neutrophil (ANC) of ≥ 1.5×109/L, platelet count of ≥ 100.0×109/L, and hemoglobin of ≥ 9.0 g/dL (with or without transfusion). * Hepatic function defined as serum total bilirubin ≤ 1.5 × ULN (\<3 x ULN in patients with Gilbert's syndrome), AST/ALT ≤ 2.5 × ULN (or ≤ 5 × ULN in patients with liver metastases). * Renal function defined as creatinine clearance ≥ 30 mL/min by Cockcroft Gault equation. * Cardiac function with Left Ventricular Ejection Fraction (LVEF) ≥ 50%. 6\. Female patients must be surgically sterile (or have a monogamous partner who is surgically sterile) or be at least 2 years postmenopausal or commits to use 2 acceptable forms of birth control (defined as the use of an intrauterine device, a barrier method with spermicide, condoms, any form of hormonal contraceptives) or abstinence for the duration of the study and for 4 months following the last dose of study treatment. Male patients must be sterile (biologically or surgically) or commit to the use of a reliable method of birth control (condoms with spermicide) for the duration of the study and for 4 months following the last dose of study treatment. 7\. Female patients who are women of childbearing potential (WOCBP) must have a negative serum pregnancy test at Screening within 7 days of dosing with CTX-10726. 8\. Prior anticancer therapy \> 28 days (or 2 half-lives for proteins, whichever is shorter), radiotherapy \> 7 days (concurrent localized palliative radiotherapy is allowed during CTX-10726 treatment with medical monitor approval), therapeutic surgical intervention \> 21 days, blood transfusion \> 14 days, or biopsy or minor surgery (excluding placement of vascular access devices) \> 7 days prior to the first dose of CTX-10726. 9\. Resolution of all prior anti-cancer therapy toxicities ≤ Grade 2 (excluding alopecia). 10\. Capable of understanding and complying with protocol requirements 11\. Signed and dated institutional review board (IRB) approved informed consent form (ICF) before any protocol-directed screening procedures are performed. Exclusion Criteria: 1. Developed clinically significant adverse reaction to prior PD-1 or PD-L1 therapy, including immune related adverse reactions (irAE), that led to discontinuation of treatment. A prior irAE may be considered not exclusionary only after consultation with the Medical Monitor if it resolved or stabilized to Grade 1 or baseline before informed consent, has been clinically stable for at least 3 months, and does not require ongoing systemic corticosteroids or other systemic immunosuppressive therapy other than protocol-permitted physiologic replacement. Participants are not eligible if the prior irAE was severe or life-threatening, involved a high-risk organ system with potentially dangerous recurrence, was recurrent or occurred after rechallenge, required second-line immunosuppressive therapy beyond corticosteroids, suggested broad immune susceptibility, or could confound safety evaluation in this first-in-human study. 2. Prior organ transplantation. 3. History of arterial or venous thrombosis or stroke or transient ischemic attack within 6 months prior to the first dose. 4. History of other neoplasms within 3 years prior to screening, except basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or cervical cancer in situ that has undergone successful surgery. 5. Symptomatic or uncontrolled central nervous system (CNS) and brain metastasis or active leptomeningeal disease. Patients with equivocal findings or with confirmed brain metastases are eligible for the study provided that they are asymptomatic and radiologically and neurologically stable wi