CD274 and thyroid gland undifferentiated (anaplastic) carcinoma: During PTC progression, overall immune activity increases, with significant elevations in the abundance and proportions of pro-tumor immune cells (M2 macrophages, Tregs, monocytes, neutrophils, DCs, MCs, and M0 macrophages) (33).Additionally, most anaplastic thyroid carcinoma (ATC) tumor cells are PD-L1 positive, and their TME is enriched with PD-1/PD-L1-positive infiltrating lymphocytes.