PDCD1 and classic Hodgkin lymphoma: The continued success of immunotherapy in solid tumors has prompted its use in hematologic malignancies, and PD-1 blockade has shown promising preliminary results in classical Hodgkin lymphoma (cHL) (Hodi et al., 2010; Topalian et al., 2012; Robert et al., 2014; Younes et al., 2016).