Immunohistochemical Analysis of PD-L1 Expression

PD-L1 expression was analyzed by immunohistochemical staining of tissue microarrays (TMAs) of the respective primary tumors as previously described [20 (link)]. Briefly, to create TMAs, tissue punches were taken from the tumors, placed in paraffin blocks, and cut into thin layers before transferred to a microscope slide. Next, TMAs were stained in the CoverStainer (Dako/Agilent, Santa Clara, USA) with PD-L1 antibodies. According to the standards of the Department of Pathology, University Medical Centre Mainz, Germany, the anti-PD-L1 rabbit antibody EPR19759 (diluted 1: 250, Abcam, Berlin, Germany) was used. Tissue samples were provided by the tissue bank of the University Medical Center Mainz in accordance with the regulation of the tissue biobank and the approval of the ethics committee of University Medical Center Mainz (Project number: #GB000218).