Effects of the antiestrogen toremifene on growth of the human mammary carcinoma cell line MCF-7.

The effects of toremifene, a new antiestrogenic drug, were investigated in vitro on the exponentially growing human mammary carcinoma cell line MCF-7. The drug effects were monitored by serial cell counts and DNA flow cytometry. The inhibitory effect of toremifene on MCF-7 became greater as the drug concentration was increased from 1 microM to 10 microM. At 5 microM toremifene induced a large decrease in the relative percentages of S- and G2/M-phase cells, and an increase in the amount of cell debris, indicating increased cell death. After withdrawal of the drug the mammary cancer cells resumed logarithmic growth similar to that of control cells. The effects caused by toremifene were similar to those caused by tamoxifen both in quality and quantity.