Immunohistochemistry (IHC) is currently the most commonly used method for evaluation of PD-L1 status in cancer patients,including NSCLC. However, biopsies are spatiotemporally limited because of the highly heterogeneous expression of PD-L1. Only 20-40% of PD-L1-positive patients respond to treatment, while 10% of PD-L1-negative patients show a good response to immune checkpoint inhibitors .Patients with false-negative PD-L1 results may miss the chance for targeted therapy.Additionally, the PD-L1 status can change dynamically during the disease process.Therefore, it is necessary to achieve higher response rates, lower toxicity and lower treatment costs by finding assays to better assess PD-L1 expression and screen patients for benefit.~PD-L1 PET imaging provides a new approach to assess PD-L1 expression in NSCLC patients and is expected to overcome the limitations of immunohistochemical ,detection of PD-L1 expression for dynamic visualization in primary and metastatic tumors . First, PET imaging can provide multidimensional three-dimensional data of overall PD-L1 expression in tumors. Second, the whole-body PD-L1 expression level can be assessed, and the heterogeneity of PD-L1 expression between tumors can be studied simultaneously. Third, it is non-invasive and provides information on PD-L1 expression not only before treatment, but also allows monitoring PD-L1 expression several times during treatment ,to screen patients for benefit and guide treatment.~Currently, the FDA-approved 68Ga/68Gagenerator is commercially available, and the cyclotron can produce 68Ga on a large scale. Also, the 68Ga labeling technology is mature. Therefore, 68Ga-PDL1 PET imaging is more easily translatable to the clinical setting. A previous study reported the synthesis and preclinical evaluation of 68Ga-BMS986192, including PD-L1 affinity, metabolic stability, micro PET imaging and in vivo biodistribution in PD-L1 positive and negative transplanted tumors, demonstrating the feasibility of this tracer for in vivo imaging of tumor PD-L1 expression.
Clinical trials have shown efficacy of PD1/PD-L1 checkpoint inhibitors in multiple solid tumors, including NSCLC. Whole body information with regard to target presence, drug kinetics and dynamics, as well as binding of PD-L1 targeting agents to the immune system cells is lacking.Molecular imaging of PD-L1 could lead to new insights on heterogeneity of PD-L1 expression in metastatic lesions and be of help in the prediction of response to PD1/PD-L1 inhibitors in a noninvasive manner.