Parathyroid cancer: etiology, clinical presentation and treatment

Parathyroid carcinoma (PC) is an uncommon finding, accounting for only 1-2% of patients with primary hyperparathyroidism (HPT), but a relatively higher incidence has been reported in Italy and Japan. The etiology of the tumour remains unclear, but molecular analysis studies have hypothesised the involvement of mutations of several genes in the pathogenesis of PC, including the oncogene cyclin Dl or PRADI located at the chromosome 13, the retinoblastoma and the p53 tumour suppressor gene. The clinical presentation of patients with PC is mainly related to the increased secretion of PTH rather than to the tumour burden. The pre-operative diagnosis of malignancy is very difficult to obtain, and, thus, intra-operative recognition of PC is mandatory. However, reliable signs of malignancy are rarely detectable. Probably, only vascular invasion, that correlates with tumour recurrence and metastases, should be considered useful in confirming malignancy, although both Ki-67 and Cyclin D1 have been recently used to aid in the definitive diagnosis. The en bloc resection of the tumour, together with ipsilateral thyroid lobe and adjacent structures, only if involved, avoiding any capsular rupture of the mass, represents the gold standard of surgical treatment of patients. Although the PC has traditionally been considered as a radioresistant tumour, there are some retrospective data holding a possible benefit from post-operative irradiation. No cytotoxic regimen with proven efficacy is currently available for patients with PC, but since hypercalcemia is ultimately the most frequent cause of death, several studies have suggested the usefulness of bisphosphonates (i.e., clodronate, pamidronate and zoledronate), calcitonin, and calcimimetic agents (i.e., cinacalcet) in patients with PC and severe hypercalcemia. In conclusion, PC is a rare malignancy and the NCDB survey reports an overall five- and ten-year survival rate of 85% and 49%, respectively. However, it is very difficult to predict the clinical behaviour of patients with PC and probably the ultimate prognosis depends on successful resection of the tumour at the initial surgery.