A 51-year-old man had a malignant Leydig cell tumor of the testis with elevation of serum estrone and endrostenedione as well as urine chorionic gonadotropin. The fine structural features of the neoplasm resembled those of nontumorous Leydig cells as well as cells of Leydig cell adenomas, except for, nuclear pleomorphism, the absence of Reinke's crystals and the infrequency of microvilli. The abundance of smooth surfaced endoplasmic reticulum, well-developed mitochondria with tubular and vesicular cristae were regarded as representing ultrastructural expressions of enhanced secretory activity and consistent with the biochemical findings of increased hormonal production by tumor cells. Since Leydig cells have distinct ultrastructural features, ultrastructural investigation represents a valuable tool in establishing the Leydig cell origin of a tummor.
Cancer 49714-721, 1982.
UMORS OF LEYDIG CELLS (interstitial cells) com-
T prise 1-3% of all testicular neoplasm^.'^,^^*^^ Leydig cell tumors may secrete various steroids, most commonly testosterone, and may be accompanied by different endocrine abnormalities such as virilism or femir~ization.~~'~~'~~~~~~~*~~ They can be divided into benign tumors which grow slowly and remain small, and into malignant tumors which show a faster growth rate, reach a larger size, invade neighbouring tissue and give rise to distant metastases. Malignant testicular Leydig cell tumors are exceedingly rare. Ober et aLZ4 reviewed the literature and found 15 cases of malignant Leydig cell tumors of the testis including their own case. Additional malignant Leydig cell tummors have since been reported bringing the number of reported cases
The fine structural characteristics of a Leydig cell tummor of the human testis were first described in 1964 by Cervos-Navarro et ~l . , ~ and subsequently by other authors.z~3~5~9*'3~'4.'6.21.27.28 Leydig cell tumors occurring in various animal species have also been studied by to 22.1,6.Il,