Levels of histaminase and L-DOPA decarboxylase activity in the transition from C-cell hyperplasia to familial medullary thyroid carcinoma.

The distribution of calcitonin, L-dopa decarboxylase, and histaminase is studied in sectioned total thyroid glands from patients with different stages of familial medullary thyroid carcinoma. In 5 glands with gross carcinoma and in 3 with early microscopic carcinoma the distribution of all three parameters positively correlates (p less than .01 for each correlation). In contrast, in 6 glands with C-cell hyperplasia only the distribution of calcitonin and L-dopa decarboxylase correlates (r = 0.64, p less than .01) while those for histaminase vs. calcitonin (r = .17, p = N.S.) and histaminase vs. dopa decarboxylase (r = .03, p = N.S.) do not. In the glands with microscopic carcinoma the peak levels of histaminase occur in the areas of disease as defined by immunohistochemical staining of calcitonin; mean histaminase activity is the only one of the three parameters measured that distinguishes between C-cell hyperplasia and microscopic carcinoma (p less than .005). Immunohistochemical staining of histaminase shows positive cells in glands with gross and microscopic carcinoma, but in none of the glands with hyperplasia alone. Histaminase is thus found in high amounts in some malignant C-cells only and may be a useful marker to distinguish between hyperplasia and malignancy in thyroids with early C-cell proliferative disorders.