Ultrastructural localization of endogenous peroxidase (peroxidase) in differentiated thyroid carcinoma was studied in 2 cases of follicular carcinoma and 12 of papillary carcinoma. The reaction product for the enzyme was observed in cancer cells which had a round and smoothly-contoured nucleus and rather few number of microvilli (positive cells) and the product localized mainly in the rough-surfaced endoplasmic reticulum and perinuclear cisternae. The positive cells resembled normal follicular cells in localization sites of the reaction product and ultrastructural features. On the contrary, in cancer cells having an irregularly-outlined nucleus with or without intranuclear cytoplasmic inclusion and many microvilli, no reaction product was visualized (negative cells). The positive cells were frequently found in 2 follicular carcinomas and 2 papillary carcinomas. Only a few number of positive cells presented in 2 papillary carcinomas. The remaining 8 papillary carcinomas were composed only of negative cells. Histologically, follicles with colloid were frequently found in carcinomas with abundant positive cells, whereas they were few in number in carcinomas containing only negative cells. These findings suggest that loss of peroxidase activity in cancer cells of follicular cell origin correlates with anaplastic change of the cancer cells.
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Yamashita et al. (1987) studied this question.