[Cytomorphological and cytochemical studies of experimentally-induced thyroid tumors in the rat]

Abstract

Carcinomas were induced to the thyroid gland of female rats, using a method originally proposed by Thomas and Bollmann (metachronous application of nitrosomethylurea and methylthiouracil), to establish cytomorphological, histomorphological, cytochemical, and flow-cytophotometric criteria for diagnosis of thyroid carcinoma. Verification was also intended of the diagnostic value of each of the methods involved for differentiation of nodular goitre. Another purpose of the study was to find out, whether chemically induced thyroid tumours in rat were comparable to thyroid neoplasms in man. This provided to the examiners genetically coherent and morphologically comparable biological material at various stages of thyroid tumour growth which included diffuse and adenomatous hyperplasias, adenomas, and, from the 18th to 42nd experimental weeks, papillary as well as follicular carcinomas in 31 to 100% of all experimental animals involved. Cytomorphological comparability of rat thyroid material (imprint specimens) with human material (fine-needle aspiration cytology) was ensured for normal as well as for hyperplastically altered thyroid glands, including adenomatous and carcinomatous changes. Hence, group typing of thyroid cytology, originally devised for human specimens, could be easily adapted to material obtained from rat. Assessment of cytological samples by microscopic criteria yielded an accuracy of 89% in malignoma diagnosis and proved to be an approach of highly informative potential also in the context of rat experiments. Use of additional cytochemical techniques (PAS, toluidine-blue, peroxidase, alkaline and acid phosphatases, gamma-glutamyl transpeptidase) as well as quantitative DNA determination by means of flow-cytophotometry was helpful in casting light at some scattered trends of change from normal for certain stages of proliferation, but it failed to enhance information in cytomorphological diagnosis of the individual case.