The depletion of T-cell response could be driven by ARG2 (Arginase 2) upregulation, which was found in BC BMs and confirmed immunohistochemically (ARG2 protein expression was associated with worse breast–brain metastasis-free survival (p = 0.027) and OS (p = 0.019)), so ARG2 could be another potential marker of BC distant metastasis and a therapeutic target in BC BM, as proposed by authors [50]. Here, ARG2 is linked to breast cancer.