Leydig cell tumor of the testis. Morphological and endocrinological investigations in two cases.

Clinical, morphological and endocrine characteristics of 2 patients with Leydig cell tumours (1 benign unilateral and 1 malignant bilateral) are reported. The morphological investigation revealed that the neoplastic cells had the same ultrastructural characteristics as normal Leydig cells. The only ultrastructural difference was the presence of 'membranous whorls' that have never been found in normal human Leydig cells. The patient with benign unilateral Leydig cell tumour appeared to produce no excess of steroid hormones, but rather a substance of FSH-inhibiting activity. The second patient, with the malignant bilateral tumours however, besides producing large amounts of testosterone, oestradiol-17 beta and progesterone, showed typical signs of an ectopic ACTH syndrome. The endocrinological and morphological features are discussed.