[en] Despite its intensive use in adjuvant breast cancer therapy for more than 30 years, the exact mechanisms of action of tamoxifen have not yet been fully characterized. Tamoxifen was recently shown to restore the E-cadherin function of human breast cancer MCF7/6 cells and to suppress their invasive phenotype. Because tamoxifen interacts with targets implicated in Ca2+ homeostasis, we explored the possibility that the restoration of E-cadherin function in MCF7/6 cells induced by this drug could be affected by Ca2+ modulators. Two different Ca2+ channel antagonists (verapamil and nifedipine) potentiated the effect of tamoxifen on E-cadherin function, as evaluated with a fast cell aggregation assay. These molecules decreased the tamoxifen concentration needed to restore the E-cadherin function from 10(-6) M to 10(-7) M. When incubated with a Ca2+ channel agonist, Bay K8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoro-methylphenyl)- pyridine-5-carboxylate), the effect of tamoxifen on E-cadherin function was completely abolished. These results demonstrate that the restoration of the E-cadherin function induced by tamoxifen depends, at least in part, on a Ca2+ pathway, and support the evidence of an effect of tamoxifen on Ca(2+)-dependent mechanisms. Our data also suggest that Ca2+ channel modulators could make it possible to decrease the dose of tamoxifen administered to patients without reducing the therapeutic effects.