TAMs (CD11b+F4/80+) constituted the major population of CD45+ tumor‐infiltrating leukocytes (TILs) in the 4T1 mammary carcinoma model (Figure 1f), which was consistent with evidence reported in several studies.[qv: 3,14a] Although PLG‐CA4 did not affect the total TILs and TAMs cell population in tumors, it enhanced the accumulation of immunosuppressive M2‐like (CD11b+F4/80+CD206+) state (Figure 1f), indicating that PLG‐CA4 treatment induced macrophage polarization to TAM‐M2 phenotype (Control 30% vs PLG‐CA4 53%; p < 0.05). Here, MRC1 is linked to breast carcinoma.