Light and electron microscopy of parathyroid carcinoma. Report of three cases.

Abstract

The morphology of three cases of parathyroid carcinoma is described, including the electron microscope findings in two of these cases. The clinical and morphologic points for the tentative diagnosis of parathyroid carcinoma are discussed. The malignancy of a parathyroid tumour is proved by lymphogenic or hematogenic metastases, by histological evidence of tumour infiltration into the surrounding tissues (including macroscopic adherence and sometimes vocal cord paralysis), and by cytologic evidence of mitoses. Nuclear atypism is often present but is neither a necessary nor an adequate proof of malignancy, because it is also seen in benign adenomas and in hyperplastic parathyroids. The ultrastructure of the carcinoma cells was also characterized by nuclear atypism and mitoses. In one carcinoma, the contents of cytoplasmic organelles varied in different cells, indicating various endocrine activity of the tumour cells. In another parathyroid carcinoma with low endocrine activity, copious cytoplasmic organelles and many secretory granules were found. There seem to be three possible causes of non-functioning parathyroid carcinomas: 1. lack of hormone synthesis, 2. impairment of cellular hormone secretion, 3. synthesis of a pathologic protein with defective endocrine activity.