OBJECTIVES: The objective was to test the hypothesis that uterine sarcomatous cells are hormone-sensitive. We included 2-methoxyestradiol, an endogenous metabolite of estradiol with antiproliferative properties. METHODS: Proliferation assays assessed the effects of estradiol, progesterone, tamoxifen, raloxifen, [D-Trp(6)]leuteinizing hormone-releasing hormone (LHRH), ICI 182,780 (faslodex or fulvestrant), and 2-methoxyestradiol on cell growth of a cell line derived from uterine carcinosarcoma, but consisting solely of mesenchymal cells (SK-UT-1). Morphological changes of SK-UT-1 cells after exposure to 2-methoxyestradiol were evaluated and fluorescence immunohistochemistry for tubulin was used to detect changes in the mitotic spindle. Flow cytometry was used to assess the influence of 2-methoxyestradiol on the SK-UT-1 cell cycle as well as the role of p53 in apoptosis. RESULTS: Cell proliferation analysis revealed that SK-UT-1 cells were stimulated by progesterone, tamoxifen, and [D-Trp(6)]LHRH. Cells were insensitive to estradiol, raloxifen, and ICI 182,780. Inhibition occurred after exposure to 2-methoxyestradiol and was accompanied by a threefold increase in the G2/M population, with a concomitant decrease in the G1 population, as shown by cell cycle analysis. SK-UT-1 cells exposed to 2-methoxyestradiol showed morphological changes indicative of apoptosis. Examination of signaling pathways that mediate 2-methoxyestradiol-induced apoptosis showed p53-independent growth inhibition. The inhibition of SK-UT-1 cell growth by arresting the cells during G2/M progression could be attributed to interference with the microtubule system, as determined by fluorescence immunohistochemistry. CONCLUSIONS: The stimulatory effect of progesterone, tamoxifen, and [D-Trp(6)]LHRH suggests that uterine sarcomatous cells are hormone-sensitive. Our finding that 2-methoxyestradiol-mediated growth inhibition of uterine sarcomatous cells occurred in a p53-independent manner may have considerable clinical significance. The inadequate armature against uterine sarcomas and the limited toxicity of 2-methoxyestradiol may render these observations especially important.