Abstract Introduction: Breast cancer is the second-leading cause of oncology-related death in US women. Despite extensive research, over 30% of breast cancer patients develop metastatic disease, and metastases account for majority of breast cancer-associated morbidity and mortality. Of all invasive breast cancers, patients with tumors lacking expression of the Estrogen and Progesterone hormone Receptors and Human Epidermal growth factor Receptor 2 have the poorest clinical prognosis. These triple-negative tumors (TNBC) represent an aggressive form of the disease that is marked by an early-onset metastasis, a high tumor recurrence rate, and a low overall survival during the first three years post-diagnosis. However, few TNBC mouse models of metastasis currently exist. Results: We noticed that a well-established MDA-MB-231 TNBC cell line produces rapid and extremely lytic bone lesions in lumbar, sacral and caudal vertebrae, and hind limbs in about 10% of animals injected intravenously. We biopsied one of these bone metastases and established a new metastatic MDA-MB-231-1566 cell line. Following an intravenous injection, MDA-MB-231-1566 cells produce early-onset metastasis to bone in up to 70% of animals with concurrent metastases to lungs, liver, and soft tissues. We demonstrate that 100% of animals injected with MDA-MB-231-1566 cells developed metastasis and had median survival of 60 days vs. 80 days in mice injected with the parental cell line. We also demonstrate that ribosomal protein S6 is highly phosphorylated on Ser235/236 in metastatic TNBC tumors, and that this phosphorylation is indicative of upstream S6 kinase (S6K) activity. Lastly, we provide evidence that targeting S6K with a highly specific inhibitor, PF-4708671, at sub-lethal doses inhibits cell migration without inducing cell death, and thus may provide a potent anti-metastatic adjuvant therapy approach. Conclusion: We established a new model of rapid TNBC metastases to multiple organs following a simple intravenous injection. We believe this model provides a valuable tool for screening new therapeutics aimed to stop growth of metastases. Citation Format: Yekaterina B. Khotskaya, Aarthi Goverdhan, Jia Shen, Mariano Ponz Sarvice, Shih-Shin Chang, Ming-Chuan Hsu, Yongkun Wei, Weiya Xia, Patricia Steeg, Dihua Yu, Mien-Chie Hung. S6K1 promotes invasiveness of breast cancer cells in a novel model of triple-negative breast cancer metastasis. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A49.