Antiestrogens in treatment of breast cancer

The antiestrogens represent a group of compounds, not necessarily steroidal, which are able to decrease the specific uptake of estrogens in vitro and in vivo by various target tissues in the rat and in man. This action is explained either by competitive binding to estrogen receptor sites or, more probably, by failure of the antiestrogen complex, translocated into the nucleus, to stimulate neoformation of receptors in the cytoplasm. This explains the transient estrogenic effect of antiestrogen. Antiestrogens used in humans are hormone specific and antagonize also non-steroidal estrogens, like stilbestrol. Three compounds have been used in advanced breast cancer with the same indications as the older hormonal treatments. They are clomiphene citrate, nafoxidine and tamoxifen. Nafoxidine and tamoxifen are probably equally active. The response rate is between 28 and 35%, with a median duration of nine months. Nafoxidine is toxic for the skin and tamoxifen is the preferred compound. A randomized trial comparing ethinyl estradiol and an antiestrogen showed similar rates of response with the two compounds in advanced breast cancer. The uniformity of results of treatment of advanced breast cancer by hormonal agents including antiestrogens and their limitations, probably justifies the present-day concept which assigns hormonal treatment a secondary role, either as a supplement to cytotoxic chemotherapy or for old and debilitated patients. However, as a supplemented to chemotherapy, hormonal agents are probably important since recent studies have shown that apparently all breast cancers have positive receptor sites, albeit in variable amounts. Because of their lack of toxicity, antiestrogens are probably the best hormonal agents available at present.