Sasse S, Reddemann K, Diepstra A, Borchmann S, Oschlies I, Schnitter A, Engert A, Borchmann P, Klapper W. Programmed cell death protein1 (PD1)-expression in the microenvironment of classical Hodgkin lymphoma at relapse after conventional chemotherapy and at relapse on anti-PD1 treatment. Haematologica 2018; 104(1):e45-e46; https://doi.org/10.3324/haematol.2018.207829.