A potential role for LIF in the pathogenesis of human breast cancer is indicated by its expression in breast cancer cells [3,4], which can be modulated by progestins and antiprogestins [5], and by its capacity to induce the proliferation of several estrogen-dependent (MCF-7 and T47D) and estrogen-independent (SK-BR3 and BT20) breast cancer cell lines as well as fresh breast carcinoma cells [4,6]. The gene discussed is LIF; the disease is breast carcinoma.