The potential for the anti-breast cancer drug tamoxifen [(Z)-1-[4-[2-(dimethylamino)ethoxy]phenyl]-1,2-diphenyl-1-butene] to induce genotoxic damage (DNA adducts) in the human endometrium was investigated in vivo and in vitro. Endometria from hysterectomy patients who were not on tamoxifen were sectioned and maintained in short-term organ culture. The cultures were treated with either solvent vehicle (DMSO), tamoxifen, α-hydroxytamoxifen [(E)-1-[4-[2-(dimethylamino)ethoxy]phenyl]-1,2-diphenyl-1-buten-3-ol; the major DNA-reactive metabolite in the rat], or benzo(a)pyrene. DNA was isolated and analyzed by 32P postlabeling. Chromatography on polyethyleneimine-cellulose TLC plates revealed DNA adducts in endometria treated with α-hydroxytamoxifen identical to those seen previously in the rat liver. However, no adducts were seen from treatment with tamoxifen itself. The viability of the enzyme-metabolizing systems of the endometrial samples was demonstrated by the detection of expected DNA adducts induced by benzo(a)pyrene. Examination by liquid chromatography-mass spectrometry of the explant culture media from endometria treated with tamoxifen revealed the presence of the α-hydroxy metabolite in a dose-dependent manner, although apparently at levels insufficient to produce detectable DNA adducts. Endometrial DNA obtained from 18 patients undergoing daily treatment with 10–40 mg tamoxifen for 3 months-9 years was also analyzed. No evidence for any DNA adducts induced by tamoxifen was found in any of the patients examined. These data suggest that the genotoxic events observed with tamoxifen in the rat may not apply to the human endometrium.

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This work was supported by the Cancer Research Campaign.

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