New aspects of steroid hormone dependent tumor growth.

Steroids are able to modulate tumor growth. These mechanisms involve probably a complex network of events which earlier were thought to be rather independent of each other. This review summarizes some new results in steroid hormone research, concerning its influence in understanding of tumor growth, above all estrogen dependent mammary tumor growth. It focuses on the following main topics situated in the centre of research at present. 1. Steroid receptors triggering the biological action of steroids are members of a superfamily of transcriptional activators with potential growth modulating properties. The DNA-binding domain of these different proteins is highly conserved. Tumor cells possibly use some of these molecules for their own growth. 2. Hormone dependent mammary tumor growth includes probably a very complex interaction of steroids with their nuclear receptors, growth factors and their membrane receptors, proteolytic enzymes and others. Tumor cells are able to secrete a lot of different proteins in response to estradiol.