FOXP3 and neoplasm: In triple-negative breast cancer (TNBC), high infiltration of CD25^hi FOXP3+ 4-1BB+ effector Tregs (eTregs) is linked to immune evasion and resistance to PD-1 blockade therapies (23, 24), representing a terminally differentiated and metabolically active subset with strong suppressive capacity that sustains an immunosuppressive tumor milieu and limits antitumor T cell activity (24).