PDCD1 and diffuse large B-cell lymphoma: While some studies observed that PD-1+ tumor-infiltrating lymphocytes (TILs) are associated with favorable clinical outcome in DLBCL (Muenst et al., 2010; Ahearne et al., 2014; Kiyasu et al., 2015; Fang et al., 2017), a recent study by Enemark et al. showed that PD-1 on intrafollicular T cell is a predictive biomarker for histological transformation of FL into DLBCL (Beck Enemark et al., 2021).