The DNA component of neutrophil extracellular traps (NET-DNA) is associated with cancer metastasis and chemotherapy resistance. However, recent studies have suggested that NET-DNA contributes to the activation of dendritic cells (DCs) and promotes the innate immune response to anticancer immunity. Therefore, exploring therapeutic approaches to inhibit NET-mediated tumor progression while maintaining antitumor immunity is essential. Our groups recently identified CCDC25 as a specific NET-DNA sensor on the cytoplasmic membrane of cancer cells that promotes cancer metastasis. In this study, we performed small-molecule compound screening and revealed that mitoxantrone (MTO) could block the interaction between NET-DNA and CCDC25. Molecular docking results indicated that MTO competed with NET-DNA by binding with the amino acid residues Tyr(24) (Y24), Glu(25) (E25), and Asp(28) (D28) of the crystal structure of CCDC25. More importantly, we conjugated MTO with palmitoleic acids such as di-Pal-MTO to increase its residence time on the cytoplasmic membrane, which increased its inhibitory efficiency and decreased its cytotoxicity. In addition, di-Pal-MTO markedly inhibited the RAC1-CDC42 cascade to alleviate the NET-induced cytoskeleton arrangement and chemotactic migration of cancer cells. In multiple mouse models, di-Pal-MTO can suppress breast cancer metastasis and have synergistic effects with chemotherapeutics. Moreover, di-Pal-MTO promotes NET-DNA-dependent DC activation, leading to the subsequent expression of various chemokines that facilitate the infiltration of CD8(+) T cells. Overall, we successfully identified a small molecule inhibitor, di-Pal-MTO, with dual effects on tumor repression and the antitumor immune response, which provides a novel therapeutic strategy against breast cancer.