Stephanie Sasse, Katharina Reddemann, Arjan Diepstra, Ilske Oschlies, Antje Schnitter, Sven Borchmann, Andreas Engert, Peter Borchmann, Wolfram Klapper. Programmed cell death protein-1 (PD-1)-expression in the microenvironment of classical Hodgkin lymphoma at relapse during anti-PD-1-treatment. Haematologica 2018;104(1):e21-e24; https://doi.org/10.3324/haematol.2018.196279.