Although many studies have revealed that PD-1 and programmed cell death-ligand 1 (PD-L1) are highly expressed in HT tissues 34, 48, 79, 80 regardless of whether differentiated thyroid carcinoma (DTC) coexists, it seems to be the response to HT conditions in the immune microenvironment. Here, PDCD1 is linked to hematocrit.