Parathyroid carcinoma as a challenging diagnosis: report of three cases.

Parathyroid carcinoma (PC) is a rare malignancy with an indolent but progressive course. This rare tumour is often difficult to diagnose preoperatively, thus limiting the efficacy of surgery. As long-term survival is largely dependent on the extent of the primary surgical resection, it is of great importance to consider PC in the differential diagnosis of hyperparathyroidism. We herein report three PC patients with different clinical histories who were followed up at our hospital for over a 5-year period, emphasizing the variability in clinical presentation of this rare tumour. Moreover, NORA (Nucleolar Organizer Regions, a standardised silver-stain, marker of proliferation rate) values encountered in these PC patients confirm that AgNOR analysis may be regarded as an additional tool when the pathologist encounters difficulties in defining parathyroid lesions which are not clearly benign.