This study introduces an innovative approach to treating incurable cancers, particularly triple-negative breast cancer, by developing a Selective Anticancer Complex (SAC). The SAC combines Cancer-Growth Inhibiting (CGI) siRNA with a novel Selective Anticancer Peptide (SAP), forming spontaneously through electrostatic attraction. This innovative complex not only enhances the stability and delivery efficiency of CGI siRNA but also exhibits a synergistic anticancer effect. Unlike traditional approaches where peptides serve merely as carriers or separate therapeutic agents, SAC integrates both delivery and therapeutic functions. The complex demonstrates remarkable selectivity, significantly reducing the viability of specific cancer cell lines like MDA-MB-231 while sparing normal cells. Animal studies corroborated these findings, showing statistically significant tumor size reduction in MDA-MB-231 xenografts. This research represents a significant advancement in cancer therapeutics, offering a safe and promising treatment option for triple-negative breast cancer, for which selective treatments are currently lacking. By successfully combining the gene-silencing capabilities of CGI siRNA with the anticancer properties of SAP, this study opens new avenues for designing multifunctional, selective anticancer therapies, potentially revolutionizing the approach to treating aggressive and resistant cancers.