In a mouse model of colon carcinoma, compared to nontargeted nanoparticles, nanoparticles that had been modified with CXCR4 antagonists had a higher affinity for cancer cells, an improved cellular uptake and cytotoxicity of the nanoparticles, and showed a greater aggregation at tumor sites; these events activated the immune response against the tumor. This evidence concerns the gene CXCR4 and cancer.