Comparative evaluation of PD‐L1 expression in cytology imprints, circulating tumour cells and tumour tissue in non‐small cell lung cancer patients oleh Mustafa Abdo, Yassine Belloum, David Heigener, Lutz Welker, Sönke vonWeihe, Milena Schmidt, Nadine Heuer‐Olewinski, Iris Watermann, Marlen Szewczyk, Jolanthe Kropidlowski, Thais Pereira‐Veiga, Hatice Elmas, Sven Perner, Stefan Steurer, Harriet Wikman, Klaus Pantel, Martin Reck