Significance During metastasis, hypoxia is a major force driving primary tumor cells to disseminate into the circulatory system. The key factors that promote circulating tumor cells (CTC) dissemination and allow them to successfully colonize distal sites are still incompletely known. We found that down-regulation of DSG2 in hypoxic tumor allowed single tumor cell dissemination, while DSG2-expressing tumors generated more CTC clusters. Reinduction of DSG2 expression in single CTCs may contribute to CTC survival and colonization in distant organs. These findings highlight the importance of DSG2 in breast cancer progression and metastasis.