Immune Checkpoint Blockade Therapy Using 18F-FLT PET/CT

Inclusion Criteria: * Patients must have histologically or cytologically confirmed diagnosis of cancer. * Patients who are planned to receive checkpoint blockade therapy, per referring oncologist. * Life expectancy ≥ 6 months and \< 5 years. * Disease that is measurable per RECIST 1.1. * Age ≥18 years. * Ability and willingness to provide informed consent * Women of child-bearing potential must have a negative urinary or serum pregnancy test within 7 days of each imaging time point. Exclusion Criteria: * Patient receiving other investigational radiotracers within 14 days prior to FLT and FDG imaging time points. * Patients receiving ICB in combination with chemotherapy. * Immunosuppressive therapy including systemic corticosteroids except for maintenance dosing for adrenal insufficiency. Patients requiring immunosuppressive therapy during the study will no longer be eligible. * Known additional malignancy that is progressing or requires active treatment with the exceptions of basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or in situ cervical cancer that has undergone potentially curative therapy. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, autoimmune diseases, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements * Patients with a pacemaker, stainless steel aneurysm clip or any other magnetic resonance (MR) contraindicated implant or foreign body would warrant exclusion from this study. Pacemakers may be reprogrammed or turned off by the strong MRI magnetic field. Radio-frequency (RF) fields in MR can also cause severe heating of pacemaker lead tips. Steel aneurysm clips are prone to torque in the strong MR field which can displace the clips and may damage the vessel, resulting in hemorrhage, and/or death. * Pregnant women are excluded from this study