PURPOSE: Lappaol F (LAF), a lignan extracted from RESULTS: LAF significantly inhibited the growth of MDA-MB-231 tumors, with downregulated tumor level of vimentin and upregulated level of ZO-1. In MDA-MB-231 and Hs-578T cells, LAF markedly suppressed cell proliferation, migration and invasion, and promoted apoptosis. Similarly, LAF increased the expression of ZO-1 and occludin proteins in MDA-MB-231 cells, and inhibited the expression of vimentin, snail and slug proteins in MDA-MB-231 and Hs-578T cells, as well as the expression of N-caderin in Hs-578T cells. Moreover, LAF also inhibited the phosphorylation of GSK-3β, thereby inhibited the downstream nuclear translocation of β-catenin and the expression of YAP. Furthermore, LAF significantly inhibited the expression of PI3K and AKT, and the phosphorylation of downstream mTOR. CONCLUSION: LAF showed anti-TNBC effect both