Objective: To study the clinicopathologic characteristics of parathyroid carcinoma (PTC).
Methods: Eleven cases of PTC encountered during the period from 1994 to 2012 were enrolled into the study. Forty cases of parathyroid adenoma (PA) were also retrieved for comparison. The clinical manifestations, laboratory results and pathologic features were analyzed, with literature review.
Results: The main clinical manifestations of PTC included neck mass (11/11), hypercalcemia (11/11) and hyperparathyroidism (11/11). Most patients also had osteoporosis (10/11). In contrast, PA often manifested as hypercalcemia (40/40) and hyperparathyroidism (40/40). Histologic examination of PTC showed that the tumor cells contained clear to eosinophilic cytoplasm and separated by dense bands of fibrosis. The tumor mass was surrounded by thick fibrous capsule. Foci of capsular invasion and vascular permeation were identified at the tumor periphery in all cases. Cellular atypia was not conspicuous but mitotic figures and coagulative necrosis were easily identified. On the other hand, PA were composed of tumor cells with clear to eosinophilic cytoplasm, forming glands, trabeculae or nests. Most of them (35/40) had intact fibrous capsule. Mitotic figures were rarely encountered and tumor necrosis was absent. Immunohistochemical study showed that the tumor cells in PTC were positive for CK19 (11/11), chromogranin A (9/11), synaptophysin (7/11) and parathyroid hormone (11/11). They were negative for thyroglobulin, TTF-1 and calcitonin. The Ki-67 index was less than 10% (range = 2% to 9%). In contrast, the tumor cells in PA were positive (40/40) for CK19, chromogranin A, synaptophysin and parathyroid hormone. They were negative for thyroglobulin, TTF-1 and calcitonin. The Ki-67 index was less than 3%. Follow up-data were available in 9 cases of PTC (duration of follow up = 11 months to 224 months) and 7 of the patients were still alive. Follow up of all PA cases showed no evidence of recurrence.
Conclusions: PTC is a rare malignant endocrine tumor presenting as neck mass. Histologic features suggestive of malignant behavior include presence of coagulative tumor necrosis and capsular/vascular invasion. It needs to be distinguished from other entities such as parathyroid adenoma, papillary thyroid carcinoma and medullary thyroid carcinoma.