When compared with gliomas, which seem to be infiltrated predominantly by tumor-associated macrophages (TAMs), brain metastases from other cancer types (melanoma brain metastases, in particular) are infiltrated largely by CD4+ and CD8+ T-cells.34, 35, 36 Many studies have reported that expression of Foxp3 not only occurs in Tregs, but also occurs weakly in activated T-cells and it would be difficult to distinguish these subpopulations by standard IHC.37 Here, CD4 is linked to central nervous system cancer.