MMP9 and breast cancer: Therefore, our findings collectively indicate that PCNA-associated hub proteins, especially ATM, HDAC1, and MDM2, and TNF-α-associated hub proteins, particularly CASP3, IL2, MMP9, and TNF-α, may act as critical modulators of the infiltration of six major immune cell types within the breast cancer TME, suggesting that skimmianine exerts its immunoregulatory effects by orchestrating their recruitment and activation.