Endometrial Stromal Polyps Research Articles

Variability in the rates of some common naturally occurring tumors in Fischer 344 rats and (C57BL/6N x C3H/HeN)F1 (B6C3F1) mice.

Variability inthe incidence rates of some common naturally occurring tumors for 72 inbred F344 rat and 54 (C57BL/6N x C3H/HeN)F1 (B6C3F1) mouse control groups used in carcinogenesis bioassays was evaluated. Significant heterogeneity of control rates was observed in at least two of six laboratories for lymphomas-leukemias, liver tumors, and pituitary tumors in the male rat and for pituitary tumors and endometrial stromal polyps in the female rat. Significant interlaboratory heterogeneity was observed for several tumor types in the F344 rat. In contrast, control incidence rates for tumors of the lung and liver and lymphomas-leukemias in B6C3F1 mice were relatively homogeneous within four of five laboratories. Significant interlaboratory heterogeneity was observed, however, for these mouse tumors. The causes of significant heterogeneity in naturally occurring tumor incidence rates within and among laboratories are unknown. Although the most appropriate and important comparison of an experimental group is with its matched control, there may be instances in which the historical control rates provide relevant data needed to clearly interpret carcinogenesis bioassay results. With the use of data from bioassays of 4-chloro-m-phenylenediamine and nitrilotriacetic acid, two examples are presented to demonstrate the usefulness of the historical control data.

Neoplastic and nonneoplastic lesions in aging osborne-mendel rats

Neoplastic and nonneoplastic lesions in 975 male and 970 female Osborne-Mendel rats used as controls in carcinogenesis tests were tabulated and evaluated. Three types of controls were considered—untreated controls (245 males, 245 females), controls administered corn oil in feed (530 males, 525 females), and controls administered corn oil by gavage (200 males, 200 females). Few neoplasms were seen in rats less than 18 months of age; the incidence of tumors markedly increased between 18 and 24 months of age. The incidence of some of the more common neoplasms, in which the combined incidence was greater than 1%, varied among the control groups, and in most cases the differences in incidences were not statistically significant. Hemangiosarcomas at all sites and C-cell adenomas of the thyroid in female rats were marginally significantly lower in controls given corn oil by gavage than in the other two groups. The occurrence of adenocarcinomas of the mammary gland was significantly higher in male controls given corn oil by gavage than in the other two groups. In untreated controls, the incidences of adrenal cortical adenomas in males and females and of pheochromocytomas in males were significantly higher than in both groups given corn oil. In rats administered corn oil in the feed, the incidences of pituitary adenomas in males and females, follicular cell adenomas of the thyroid in males, and endometrial stromal polyps in females were significantly higher than the incidences in the other two groups. The possible reasons for these differences are discussed. However, the types of tumors seen in the three control groups were morphologically comparable. The tumors observed included two types that had not previously been well characterized in Osborne-Mendel rats—malignant fibrous histiocytomas and lipomatous tumors of the kidney. Incidences of the more common nonneoplastic lesions are reported.

Neoplastic and nonneoplastic lesions in aging F344 rats

Neoplastic and nonneoplastic lesions in untreated F344 rats used as controls in carcinogenesis tests were tabulated and evaluated. The most common neoplasms in 1794 male rats were testicular interstitial cell tumors, leukemias, pituitary adenomas, and adrenal pheochromocytomas. In 1754 female rats, common tumors were pituitary adenomas, mammamary fibroadenomas, uterine endometrial stromal polyps, and leukemias. A variety of less common and rare tumors were seen in almost every tissue. A few malignant neoplasms were metastatic. Nonneoplastic lesions included nephropathy, cardiomypathy, focal hyperplasias in a variety of tissues, and inflammatory lesions of the uterus. The focal hyperplasias were suggestive of the early stages of neoplasia in lung, liver, pituitary, adrenal, thyroid, and testis.