The growth and function of many tissues are influenced by hormones. Therefore it is quite understandable that hormones play a role in the development and treatment of malignant tumors. Numerous publications address this topic; however, the results of many studies are controversial and have not been unequivocally accepted. For nearly 50 years the carcinogenic effect of steroid hormones has been under debate, and their therapeutic value a matter of discussion for equally as long. The present volume concentrates on substantiated data first obtained from the study of tumors developing from hormone­ regulated or hormone-producing tissue, e.g., the thyroid, adrenal glands, prostate, and the female genital tract. Through a joint approach from the field of molecular biology, biochemistry, and histopathology, advances in the management of these tumors have been elaborated. Another exciting example is the endo­ nuclear diagnosis of adrenal tumors. Antihormones, i.e. antian­ drogens or GnRH analogues have proved to be important indeed since they exhibit a destructive effect on prostate carcinomas and breast cancer. Further improvements can be expected in the localization of hormones in tumor tissue by specific antibodies. A special chapter is dedicated to the diffuse endocrine cell system (DECS), the clinical significance of which has mainly become obvious in the gastroenteropancreatic tract.