Differentiating Atypical Parathyroid Neoplasm from Parathyroid Cancer.

INTRODUCTION: The differentiation of benign parathyroid gland atypia and true parathyroid carcinoma (PC) can be challenging. In some instances, patients are classified as having 'atypical parathyroid neoplasms' (APNs), explicitly acknowledging that the distinction between benign and malignant disease appears impossible to determine. This 'grey area' diagnosis makes rendering an accurate prognosis difficult, and clouds clinical management and treatment planning.

METHODS: We performed a retrospective chart review of all patients undergoing operation for primary hyperparathyroidism in our institution (2000-2014). Patients with a histopathological diagnosis of PC or APN were included. Demographics, clinical characteristics, and survival rates were analyzed, and analysis was conducted using SAS 9.4 (SAS Institute, Inc., Cary, NC, USA).

RESULTS: Fifty-four patients were included in the study-31 (57.41 %) with PC and 23 (42.59 %) with APN. PC versus APN was associated with higher parathyroid hormone (PTH) (p = 0.005) and with males (p = 0.002). Five-year overall survival (OS) from diagnosis was 82.64 % [95 % confidence interval (CI) 59.82-93.17] for the PC group and 93.33 % (95 % CI 61.26-99.03) for the APN group, while the 5-year recurrence-free survival rate was 59.63 % (95 % CI 36.32-76.81) in the PC group and 90.91 % (95 % CI 50.81-98.67) in the APN group.

CONCLUSION: PC and APN are distinct clinical entities with differences in tumor biology reflected in overall recurrence rates, disease-free survival, and OS. APNs present with a less accentuated biochemical profile and demonstrate an indolent clinical course compared with PCs. Efforts to improve categorization and staging of PC and APN are needed.