Although PD-L2 is expressed in a variety of immune, stromal and BC cells (Baptista et al. 2016; Asano et al. 2018) and displays up to six-fold higher affinity to PD-1 than PD-L1 (Keir et al. 2008), PD-L2-bearing EVs (PD-L2EV) have attracted less interest as a biomarker in BC or other tumor entities. Here, CD274 is linked to breast cancer.