Studies in experimental goitre: malignant change in a transplantable rat thyroid tumour

Reversibility of the malignant phenotype in monoclonal tumours in the mouse

Longterm goitrogen administration to rodents is well known to result in multiple proliferative lesions of the thyroid. The regression of these lesions on withdrawal of goitrogen has led to their neoplastic nature being questioned, and they have been regarded as 'nodules' rather than as true tumours. We have induced multiple thyroid lesions by the combined use of high dose radiation as a mutagen, together with goitrogen administration to induce prolonged TSH growth stimulation. G6PD histochemistry was used in heterozygous G6PD deficient female mice to show that all the thyroid lesions induced by this regime were monophenotypic, and therefore monoclonal in origin. The great majority of induced tumours were adenomas, a minority were carcinomas. The number of carcinomas observed was significantly lower in a group of animals from which goitrogen was withdrawn for 4 weeks prior to killing, when compared to animals killed while on goitrogen treatment. Both adenomas and carcinomas, including areas of intravascular tumour, showed morphological features of regression on withdrawal of the goitrogen. There are three key cellular changes which must occur in spontaneous thyroid carcinogenesis--escape from a growth limiting mechanism, acquisition of TSH independent growth and acquisition of invasiveness. In the natural selection of mutations or epimutations during carcinogenesis, prolonged high levels of TSH are likely to remove any selective advantage from mutations that lead to TSH independent growth. Tumours induced by a regime including prolonged goitrogen treatment may therefore develop following two rather than three key stages. They will occur with an increased frequency relative to lesions observed in spontaneous carcinogenesis, but will retain TSH dependency. We speculate that several mechanisms may lead to loss of the growth limiting mechanism, including translocation of an oncogene to the region of a TSH induced promoter. Other carcinogenic regimes may also increase the yield of tumours by creating conditions which reduce the number of essential steps required for carcinogenesis, and may involve translocation to a carcinogen inducible promoter.

Dedifferentiation of a transplantable papillary thyroid carcinoma over a 15-year period

Fischer 344 rats on a prolonged low-iodine diet developed thyroid nodules which were transplanted subcutaneously into 33 thyroidectomized rats. One graft took and gave a papillary carcinoma. Serially transplanted syngeneically at 3- to 4-month intervals, it became autonomous in third generation hosts. With electron microscopy examination it was microfollicular in year 8 and anaplastic, with totally unpolarized epithelial cells, in year 15. Basement membrane present in year 1 was no longer visible in specimens of years 8 and 15. Tight and gap junctions still present in year 8 were absent in year 15, although a few desmosomes persisted. From years 8 to 15, free ribosomes and microfilaments became more frequent, whereas the number of mitochondria and the development of the Golgi complex declined.

Surgical treatment of thyroid carcinoma in a defined population: 1960 to 1977. Evaluation of the results after a conservative surgical approach

Ninety patients from a demographically well-defined area of, on an average, 243,000 inhabitants were surgically treated for thyroid carcinoma during an 18 year period. Sixty-five of the patients had papillary carcinoma, 20 follicular carcinoma, 4 medullary carcinoma, and 1 anaplastic carcinoma. Seventy-eight patients were operated on for cure, and among them, 23 had total thyroidectomy and 55 partial thyroidectomy. Additional therapy with thyroxine was given to all patients postoperatively. None of the patients treated for cure died from thyroid carcinoma at follow-up 2 to 20 years after diagnosis. One of 42 patients (2.4 percent) primarily treated for cure with lobectomy for papillary carcinoma had local recurrence in the thyroid bed which was excised successfully. No patient treated for cure of follicular carcinoma had local recurrence. All verified recurrences except one were diagnosed within 5 years of primary operation. We conclude that local recurrence after procedures less than total thyroidectomy that are considered to be curative is unusual provided that thyroxine is given postoperatively. Thus it seems that the reported high rates of microscopic carcinoma in the contralateral lobe in patients with unilateral cancer have little clinical significance. A conservative approach in most patients with localized thyroid carcinoma is indicated because it reduces the risk of postoperative complications.

Anaplastic transformation of thyroid cancer: report of two cases and review of the literature

Transformation of well-differentiated thyroid adenocarcinoma to anaplastic cancer has been occasionally reported. Two new cases of such transformation are now described. The time interval from diagnosis to the development of anaplastic cancer was 15 years in the first patient and 10 years in the second. Both patients ultimately developed extensive bilateral pulmonary metastases and died within 6 months from the diagnosis of the transformation. Hypotheses concerning the pathogenesis of the transformation and the literature were reviewed. We believe that histopathological confirmation of recurrent and rapidly progressive thyroid tumors is necessary prior to initiation of therapy.

Anaplastic carcinoma of the thyroid: a review of 84 cases of spindle and giant cell carcinoma of the thyroid

Eighty-four cases of spindle and giant cell carcinoma of the thyroid were reviewed. This is a swiftly growing, and rapidly fatal neoplasm that generally develops in the elderly. Treatment of this disease was generally unsuccessful with a 7.1% five-year survival rate and a mean survival period of 6.2 months from the time of tissue diagnosis. In the majority of cases, areas of well-differentiated thyroid carcinoma could be identified, supporting the concept that spindle and giant cell carcinoma results from the transformation of preexisting well-differentiated thyroid carcinoma. Because of the aggressive biologic activity of this neoplasm, we treat all cases as disseminated disease at the time of presentation. Our best therapeutic results have been obtained with a combination of surgery, irradiation, and chemotherapy; however, these results still leave much to be desired. Patients with only small foci of spindle and giant cell carcinoma, at the time of diagnosis, may have a better chance of prolonged survival.