Tamoxifen induces invasion in HECD-1-treated breast cancer cells. The invasive capacity of MCF-7 cells having (a) functional or (b) antibody (HECD-1)-inhibited E-cadherin was determined in the presence of E2 (10-9 M), oestrogen-free (-E2) or tamoxifen-treated conditions (10-7 M). E2 did not significantly alter the invasive ability of MCF-7 cells in either case, whereas (b) tamoxifen treatment of HECD-1-treated cells promoted a dramatic increase in invasive capacity. Graphs are representative of three independent experiments with error bars indicating the standard deviation. *p < 0.05 versus treatment with HECD-1 antibody alone.