An antiestrogenic action of interferons in human breast cancer cells.

The antiproliferative and antiestrogenic effects of human interferon on estrogen-dependent CG-5 human breast cancer cells in vitro are reported. Fibroblast beta - interferon as well as recombinant alpha - and gamma -interferon inhibited proliferation of CG-5 cells in a dose and time - dependent fashion. In addition, they completely suppressed the two-fold increase in cell number induced by estradiol and showed an additive antiproliferative effect when used in combination with the antiestrogen tamoxifen. These antiestrogenic effects of interferons were accompanied by a reduced receptor binding of estradiol to the cells.