Abstract: Metastasis is a devastating complication in breast cancer. Cancer relapse and metastasis are associated with cancer stem cells. CircBIRC6 is a circular RNA that proposed to be involved in stemness of stem cells. In breast cancer, metastatic tumor cells have higher stem cell properties. In the present study we evaluate the expression of circBIRC6 in these cells. After development of syngenic animal model of TNBC, primary breast cancer cells named 4T1T were isolated from tumor mass. Highly metastatic tumor cells named 4T1B and 4T1L were isolated and expanded from brain metastasis lesions and lung of cancerous mice respectively. Sphere formation ability in metastatic and primary tumor cells was evaluated separately. Quantitative real-time polymerase chain reaction was performed to analyze the expression of circBIRC6 in primary and metastatic tumor cells. Our data revealed that, sphere formation ability among metastatic tumor cells was significantly higher. Surprisingly expression of circBIRC6 was significantly upregulated in these metastatic tumor cells. In comparison with 4T1T, circBIRC6 was upregulated 5.7 and 3.5 time in 4T1B and 4T1L respectively. These findings provided important insights regarding the molecular properties of metastatic tumor cells and can be used to design targeted therapeutic strategies to combat these cells.