[Predictive value of PD-L1 diagnostics]

Immuno-oncology related treatments have become standard of care for many tumor entities. Numerous additional indications are currently under investigation in ongoing clinical trials. Predictive biomarkers include microsatellite instability as well as tumor mutational burden. However, PD-L1 testing by immunohistochemistry (IHC) is already widely established as a biomarker in clinical routine for certain treatment decisions in non-small cell lung cancer, head and neck cancer and in urothelial carcinomas. More applications of that kind are expected to follow. Moreover, PD-L1 testing can provide clinicians with valuable information even if the test is not mandatory (i. e., complementary diagnostics). PD-L1 staining requires a highly specific staining over a broad dynamic range. Sensitive and specific primary antibodies and suitable staining protocols are prerequisite. Selection of appropriate patients' materials, validation and contiguous quality assurance need to meet the highest standards. There are different scoring algorithms for PD-L1 stainings which are specific to tumor entities and certain clinical decisions. The tumor proportion score (TPS) is a PD-L1 measurement which is applied, for example, to lung cancer, head and neck cancer and melanomas. Within this approach, only membranous staining of tumor cells is regarded as a significant staining. In contrast, the combined positivity score (CPS) and inflammatory cell (IC) scoring include or are restricted to PD-L1 expression in certain inflammatory cells, respectively. CPS and IC scoring are standard measurements of PD-L1 in urothelial carcinoma.