TAMOXIFEN AND INTERFERON-BETA - EFFECT OF SIMULTANEOUS OR SEQUENTIAL TREATMENT ON BREAST-CANCER CELL-LINES

The presence of steroid receptors in breast cancer is usually consider ed as a good indicator fo, responsiveness to antiestrogen treatment. H owever; not all estrogen-receptor (ER) positive tumors, respond to tam oxifen, probably owing to the natural heterogeneity of breast cancer; which after tamoxifen treatment can result in an overgrowth of selecte d ER-negative clones. Since in a previous study we found that beta-int erferon exerts an antiproliferative activity on several breast cancer cell lines, regardless of their steroid receptor status, we addressed our attention to the possibility of improving tamoifen efficacy by the addition of beta-interferon. Thus, we investigated the effect of conc omitant or sequential treatment with tamoxifen and beta-interferon on breast cancer cell lines (MCF7, T47D, MDA-MB231, BT20) characterized b y a different steroid receptor status. The results showed that beta-in terferon caused a cell growth inhibition additional to that produced b y tamoxifen, regardless of the receptor status of the cell lines. Thes e findings indicate the potential of the combined treatment with tamox ifen and beta-interferon due to the direct effect of beta-interferon o n ER-negative cells and the potentiation of tamoxifen activity in ER-p ositive cells, perhaps through the induction of steroid receptor synth esis.