WNT5A is abnormally increased in a variety of cancers including breast cancer and has an adverse effect on the prognosis. However, the biological function of WNT5A is not fully known in HER2-positive (HER2+) breast cancer. Using public clinical data, we analyzed disease-free survival (DFS) and distant metastasis-free survival (DMFS). Here, we found that abnormal WNT5A induction is a correlation with the poor prognosis of HER2+ breast cancer. WNT5A expression was also decreased by pan-HER inhibitor neratinib but not by trastuzumab. In addition, WNT5A augmented cell invasiveness of HER2+ breast-cancer cells. To find WNT5A-induced metastatic-related factors, we did a human cytokine array. The levels of GM-CSF and CXCL8 were significantly increased by WNT5A. CXCL8 also accelerated cell invasiveness in HCC1954 breast-cancer cells. The expression of CXCL8 induced by WNT5A has been significantly reduced by MEK inhibitor, binimetinib. Finally, we studied the effect of CXCR2 antagonist, SB225002, to verify the relevance of CXCL8 in WNT5A-induced cell invasion. As expected, we found that WNT5A-induced cell invasion is completely inhibited by SB225002. Taken together, we have demonstrated that WNT5A directly mediates cell invasion through the induction of CXCL8 and ultimately affects the survival rate of HER2+ breast cancer.Keywords:CXCL8; Cell invasion; HER2-positive breast cancer; WNT5A.