In our present investigation, to the best of our knowledge, we firstly showed that compared to normal controls, TMED3 was markedly up-regulated in breast cancer; that elevated TMED3 significantly clinicopathologically correlated with ER, PR, HER-2 status, lymph nodes metastases and inferior overall prognosis; and that in vitro cell lines, TMED3 was shown to promote the proliferation, migration and invasion of breast cancer cells. This evidence concerns the gene ERBB2 and breast cancer.