RITA--Registry of Industrial Toxicology Animal data: the application of historical control data for Leydig cell tumors in rats

Historical data for Leydig cell tumors from untreated or vehicle treated rats from carcinogenicity studies collected in the RITA database are presented. Examples are given for analyses of these data for dependency on variables considered to be of possible influence on the spontaneous incidence of Leydig cell tumors. In the 7453 male rats available for analysis, only one case of a Leydig cell carcinoma was identified. The incidence of Leydig cell adenomas differed markedly between strains. High incidences of close to 100% have been found in F344 rats, while the mean incidence was 4.2% in Sprague-Dawley rats and 13.7% in Wistar rats. Incidences in Wistar rats were highly variable, primarily caused by different sources of animals. Mean incidences per breeder varied from 2.8 to 39.9%. Analyses for the dependency on further parameters have been performed in Wistar rats. In breeders G and I, the Leydig cell tumor incidence decreased over the observation period and with increasing mean terminal body weight. The incidence of Leydig cell tumors increased with mean age at necropsy and was higher in studies with dietary admixture compared to gavage studies. These parameters had no effect on Leydig cell tumor incidence in breeders A and B. Animals from almost all breeders had a considerably higher mean age at necropsy when bearing a Leydig cell adenoma than animals without a Leydig cell adenoma. Studies with longitudinal trimming of the testes had a higher incidence than studies with transverse trimming. The observed dependencies and breeder differences are discussed and explanations are given. Consequences for the use of historical control data are outlined. With the retrospective analyses presented here we were able to confirm the published features of Leydig cell adenomas and carcinomas. This indicates that the RITA database is a valuable tool for analyses of tumors for their biological features. Furthermore, it demonstrates that the RITA database is highly beneficial for the definition of reliable historical control data for carcinogenicity studies on a scientifically solid basis.

Effects of MTBE on the reported incidence of Leydig cell tumors in Sprague-Dawley rats: range of possible Poly-3 results

An increased Leydig cell tumor (LCT) incidence has been reported in a study of Sprague-Dawley (SD) rats exposed via gavage to 1000 (but not 250)mg/kgday MTBE; it is unclear, however, if this finding was indeed dose-related or due to the statistical analyses not having adequately accounted for the increased survival rate in the high-dose animals and/or for multiple statistical comparisons. To address this question, we conducted Hoel-Walburg and Poly-3 analyses, using p-values of 0.01 for pair-wise comparisons and 0.005 for trend tests of common tumors. We found that MTBE does not cause a statistically significant increase in LCTs in SD rats when survival is appropriately taken into account. In addition, the original study reported some overall survival data, but did not specify which rats had LCTs. This led us to conduct separate Poly-3 analyses for the most extreme scenarios of survival age and tumor incidence to provide an illustrative example of approaches for analyzing the impact of survival rates on tumor findings in the absence of animal-specific survival data. We found this method to provide results similar to analyses using the actual data, suggesting that it can be used when full survival data are not available.

On the occurrence of Leydig cell tumors in the F344 rat

Dunning began inbreeding, what is now the Fischer F344 rat, in 1931. Because of her publications showing a low incidence of spontaneous tumors to 35 months of age, we selected the F344 rat for most of the studies in the National Cancer Institute (NCI) Bioassay Program, beginning in 1964. We were surprised by the finding that untreated male F344 rats displayed a high incidence of Leydig cell tumors of the testes beginning at about 17 months of age. The key difference between the results of Dunning and the NCI Bioassay Program was that her animals were retired breeders, whereas the NCI studies utilized virgin rats. The question of breeding was, therefore, examined as a possible protective factor. Groups of male F344 CDF/Crl rats were kept as virgin animals, or permitted access to bilaterally tube ligated female F344/Crl rats that were replaced twice over a 52-week period. At that time, all males from both groups were housed three per cage to 85 weeks when they were killed in a CO(2) atmosphere and necropsied. Sections were prepared from the fixed tissues, stained and studied by histopathology. The results were evaluated by appropriate statistical methods. Virgin and sexually active F344 rats displayed monolateral or bilateral Leydig cell tumors. There was no statistical difference between the two groups. Despite the early difference between breeding and virgin F344 rats, a control experiment failed to disclose an effect of sexual activity on the occurrence of Leydig cell cancers. This disease displays some difference in incidence in various parts of the world, with the higher socioeconomic groups having a greater incidence. Etiological factors on the occurrence of this disease in animals and in humans remain to be discovered.

Spontaneous neoplastic lesions in aged Sprague-Dawley rats

Neoplastic lesions were observed in untreated aged Sprague Dawley (SD) rats throughout their lifespan starting at 5 weeks. Their mean survival times were 89 to 105 weeks of age. The total tumor incidences were 70 to 76.7% and 87 to 95.8% in males and females, respectively. The common neoplasmas were pituitary adenoma and adrenal pheochromocytoma in both sexes, testicular Leydig cell tumor in males and mammary gland tumors, thyroidal C-cell adenoma and uterine stromal polyp in females.

Effect of individual versus group caging on the incidence of pituitary and Leydig cell tumors in F344 rats: proposed mechanism

Recently, an increase in pituitary tumor (pars distalis adenoma) incidence, and decrease in testicular interstitial cell tumor incidence, has been noted in F344 rats, in 2 year National Toxicology Program dermal and inhalation studies. One of the factors that may have contributed to this correlation is the difference in housing protocols. Rats in inhalation and dermal toxicity studies are singly caged, in contrast to other types of studies in which rats are group-caged, such as dosed-feed, dosed-water, or gavage studies. We propose that stress, related to individual caging, particularly among males, directly impairs testosterone synthesis and produces Leydig cell atrophy which leads to a feedback increase in the synthesis of luteinizing hormone by the anterior pituitary. This is followed by anterior pituitary cell functional hypertrophy, hyperplasia, and eventually neoplasia. It is known that individual caging of male rats produces a stress response associated with increased serum corticosteroids. The testicular interstitial cells (Leydig cells) have specific receptors for the glucocorticoid hormones. The Leydig cell enzyme 11-beta-hydroxysteroid dehydrogenase (11-beta-HSD) inactivates gluococorticoids; however, prolonged stress depletes this enzyme, enabling the gluococorticoids to impair steroidogenesis and eventually to lead to compensatory pituitary proliferations, including neoplasms.

Testicular cancer in blacks. A multicenter experience

BACKGROUND

The rarity of testis tumor in black patients has made the study of a large series difficult. Much of the epidemiologic and clinical information regarding this neoplasm in this population is in dispute, including data on incidence, prognosis, histologic distribution, age and stage at presentation, and side distribution.

METHODS

A retrospective review of 66 blacks with testicular tumors from seven military medical centers was performed.

RESULTS

Similar results were found for blacks with testis tumor to those of the general testis cancer population regarding prognosis, side distribution, and age of onset for nonseminoma and interstitial tumors. There is a slight increase in the expected number of interstitial tumors in blacks, but the distribution between seminoma and nonseminoma is similar to the general population. The mean age of presentation for seminoma in blacks was younger than that of the general testis cancer population. For testis tumor treated at the same institution, there was an increased delay of diagnosis in blacks compared with whites. The number of new cases of testicular cancer between 1979 and 1991 at one major center was increased for whites but not for blacks. The availability of cisplatin-based combination chemotherapy has resulted in an improved prognosis for blacks, as has already been demonstrated for white populations.

CONCLUSIONS

Testis tumor in blacks behaves similarly to testis tumor in the general population except that in blacks there are more interstitial tumors and the mean age of presentation for seminoma is younger. Further, there is an increased delay in diagnosis for blacks compared with whites, but the incidence of this tumor in this population does not appear to be increasing. Cisplatin-based chemotherapy has significantly improved survival in this population.

Non-germ cell testicular tumours in Nigerians

Non-germ cell testicular tumours are reported to be more common in peoples of Negroid and Asian descent than in Caucasians. This group of tumours comprised seven of sixteen testicular tumours seen in a ten-year period at the University of Benin Teaching Hospital, Benin City, Nigeria. However, unlike experiences elsewhere in Africa and the West Indies where paratesticular tumours accounted for a majority of these tumours, malignant lymphomas constituted over 70% of non-germinal testicular tumours in our population.

Gonadal stromal tumors: a report of the Prepubertal Testicular Tumor Registry

A total of 15 gonadal stromal tumors in prepubertal boys has been reported to the Prepubertal Testicular Tumor Registry of the Section on Urology of the American Academy of Pediatrics. Leydig cell tumors invariably are benign and patients usually present with precocious puberty when they are 5 to 9 years old. Other gonadal stromal tumors either present in infancy as a scrotal mass and exhibit a benign behavior or occur later in childhood and may be malignant.

Intrascrotal tumors in the older male

Although the greatest incidence of testicular neoplasms is in the age group 20 to 35.9% of all intrascrotal tumors occur in males over 60. They may be classified into four major groups based on the tissue origin of the tumor. The most common group comprising 50% are lymphoreticular neoplasms or lymphomas. They occur in both blacks and whites, result in a diffuse enlargement of the testis and commonly involve the epididymis and cord. Prognosis is poor and survival is usually less than two years. Germ cell tumors comprise 25% and the tumors are usually large. Most of them are the classical seminoma which has a good prognosis following orchiectomy and retroperitoneal radiation. A few are the spermatocytic seminoma which is usually benign. Three percent are teratocarcinoma with embryonal elements which is highly malignant and survival less than two years. Ten percent are tumors of gonadal stromal origin. There are two types, the Leydig cell and the more rare Sertoli cell. About one-fourth of these patients develop gynecomastia and some a decrease in libido. The prognosis is good as less than 10% of these tumors are malignant. Neoplasms of supportive and paratesticular structures comprise a heterogeneous group of benign and malignant lesions and comprise about 15% of intrascrotal tumors. Most of them have the same features as tumors of similar tissues encountered throughout the body. They are the mesothelioma or adenomatoid tumor, fibroma, rhabdomyosarcoma, leiomyoma, lipoma, liposarcoma, mucinous cystadenocarcinoma, and leiomyosarcoma. As in all intrascrotal tumors, the diagnosis, treatment, and prognosis are based on the microscopic findings after removal of the tumor.

Canine testicular tumors: epidemiologic features of 410 dogs

Histologically confirmed testicular tumors were diagnosed in 410 dogs from 12 North American veterinary university hospitals and clinics. Three tumor-cell types, Sertoli cell tumor, interstitial cell tumor and seminoma, were about equally represented. Several breeds were identified with high risk for different testicular tumor-cell types. Cytogenetic and immunogenetic studies of these dog families could offer leads applicable to familial testicular cancer in man. The multiplicity of breeds within the series suggests that, as in man, other factors, in addition to hereditary, play a role in etiology. Cryptorchid dogs appear to have a 13.6 times higher risk of testicular tumor than normal dogs. Additionally, male dogs with an inguinal hernia have an increased risk (4.7) of testis tumors. There were no detectable excesses of other urogenital anomalies or urogenital tumors among the series. The Shetland Sheepdog is suggested as an appropriate model for research into the mechanisms responsible for testicular maldescent and tumorigenesis.