Synergistic antitumour effect of a combination of toremifene and interferon-alpha on ZR-75-1 human breast cancer cells: dependence on interferon-alpha subtype.

We investigated the effect of toremifene, interferon-alpha2a, interferon-alpha2b and interferon-alpha2c, 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-alpha2a, resulting in a synergistic interaction (CI <1) for all concentrations tested. A combination of toremifene plus interferon-alpha2b resulted in a synergistic interaction (CI