CD274 and sinus histiocytosis with massive lymphadenopathy: Therapeutic use of PD-1/PD-L1 blockade in histiocytic/dendritic cell neoplasms has been reported in cases of HS, with patients responding to nivolumab at progression [50, 51]; however, given the extremely limited experience using PD-1/PD-L1 blockade in histiocytic/dendritic cell neoplasms including RDD as well as variability in PD-L1 expression as determined by immunostain alone [52], treatment of RDD with checkpoint inhibitors cannot be recommended at present