PDCD1 and cancer: Ongoing clinical trials are currently investigating the clinical utility of PD-1/L1-targeted positron emission tomography- (PET-) based imaging biomarkers, such as64Cu-WL12, 99mTc-NM-01, 89Zr-envafolimab, 18F-BMS-986192, 89Zr-durvalumab, 89Zr-labeled avelumab, 89Zr-labeled atezolizumab, 89Zr-CX-072, 89Zr-labeled atezolizumab, 89Zr-nivolumab, and 89Zr-pembrolizumab for detection of PD-1/L1 expression, T cell activation, or assessment of response to treatment in cancer patients [141, 142].