We investigated the effect of toremifene, interferon-α2a, interferon-α2b and interferon-α2c, singly and in combination for their effect on the growth of ZR-75-1 human breast cancer cells. Median effect analysis was used to determine synergistic or additive effects. Anti-proliferative studies showed that the growth of ZR-75-1 cells was inhibited to a greater extent by combination treatment with toremifene plus interferon-α2a, resulting in a synergistic interaction (CI <1) for all concentrations tested. A combination of toremifene plus interferon-α2b resulted in a synergistic interaction (CI <1) for the two highest concentrations of toremifene (10-6 and 10-7 M) and an additive effect (CI approximately equal to 1) for the lower concentrations (10-8 to 10-10 M). When toremifene was combined with interferon-α2c no additive or synergistic interaction was determined.

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