Abstract
We present the case of a 39-year-old man with Klinefelter's syndrome and a metastatic Leydig cell carcinoma in whom autonomous cortisol production induced by the interstitial cell tumor was found. Apart from the Cushing's syndrome the endocrine activity of the tumor was demonstrated by the secretion of estradiol, estrone, alkaline phosphatase, and testosterone. This is, to our knowledge, the first description of a Cushing's syndrome not caused via ACTH production but directly induced by ectopic steroid production. While being resistent to chemotherapy and radiation, the tumor responded favorably to treatment with o,p'-DDD. The reduction of tumor size was accompanied by a continuous decrease of serum markers. The etiology of the tumor is discussed in the light of the hormonal derangement caused by the genetic abnormality of Klinefelter's syndrome.