In the course of our studies for new anticancer medicinal plants, we evaluated the effects of an alcohol-water (1:1, V/V) extract of Dendrostellera lesserii (Thymelaeaceae) leaves on the growth rates of breast tumors of rats. The breast tumors were induced in a group of rats by Dimethylbenz[a]anthracene (DMBA) injection. Our data showed that daily oral feeding of the crude extract to the rats, for 20 consecutive weeks, significantly repressed the growth rates of the breast tumors. In addition, the probable effect of D. lessertii crude extract or one of its purified active components on metastasis was evaluated using wehi-164 cells. Treatment of the cells with a single nontoxic dose of the purified active component for 48 hours inhibited the adhesion of the cells to the immobilized fibronectin molecules by almost 80% compared to the untreated control cells.