CD274 and medullary thyroid gland carcinoma: In agreement with the role of PD-L1 in progression of WDTC, the analysis of nine studies totaling 423 patients (34 PDTC, 85 ATC, and 304 MTC) supports the clinical value of PD-L1 as a biomarker of aggressiveness, and poor prognosis for these three TC subtypes (Table 4) 61, 62, 75-81.