Table 1.

Elements of the tumor microenvironment of thymic epithelial tumors associated with favorable and dismal prognosis.

Favorable Prognosis
High PD-L1 expression on tumor cells (controversial) [11]
Moderate and high levels of CD3+ TILs (IHC2 or 3 vs IHC1) [11]
Higher proportion of neutrophils, Th2 cells, TILs, iDCs, CD8+ T cells [31]
Dismal Prognosis
High PD-L1 expression on tumor cells (controversial) [16]
Lower expression level of HMGB1 [9]
Higher proportion of immune macrophages, NK cells, Treg, Type II IFN response, and aDCs [31]
High tumor mutational burden [35]
Tumor-associated macrophages (further investigation is needed) [38,39,40,41,42]
HSP27 and 70 expression [42,43,44,45,46,47]
High SOX9 expression [52]

PD-L1: programmed death ligand 1, TILs: tumor infiltrating lymphocytes, Th2 cells: T helper 2 cells, iDCs: immature dendritic cells, HMGB1: high mobility group box 1, NK cells: natural killer cells, Treg: T regulatory cells, aDCs: activated dendritic cells, HSP27 and 70: Heat Shock Protein 27 and 70, SOX9: SRY-related high-mobility group box 9.