Endocrine Abstracts

Introduction: Parathyroid carcinoma (PC) is a very rare neoplasm, which has histopathological features different from those of atypical parathyroid adenomas (APA). However, the clinical course of both tumour types is similar, with the exception of the unusual metastases of the carcinoma. With this study we aim to identify those clinical-analytical and anatomopathological variables that allow us to differentiate PCs from APAs.

Material and Methods: Retrospective observational clinicopathological study of a cases series diagnosed with PC and APA in the period 2000-22. The classic histological criteria of invasion of adjacent structures, vascular permeation, perineural infiltration and/or development of metastases were used to diagnose PC. Adenomas with atypical cytoarchitectural features, but without features of invasiveness or metastasis were considered APA. Immunohistochemistry for parafibromin, PGP 9.5 and galectin-3 was performed. Post-surgical tumour recurrence was determined by detection of disease on imaging and/or by elevation of parathormone (PTH) in blood.

Results: A total of 17 patients with a mean age of 59.6 years were studied. 41.2% (n=7) were classified as PC, of which one had distant metastases, and the remaining 58.8% (n=10) as APA. No statistically significant differences were observed between PC and APA in the variables of age, sex, pre-surgical blood tests [PTH (P=0.5) and calcemia (P=0.5)], ultrasound characteristics, percentage of post-surgical cure (P=0.3) and recurrence of hyperparathyroidism (P=0.6). The case of metastatic PC showed no differential histopathological features. Immunohistochemically, 29.4% (n=5) showed loss of parafibromin, of which 2 corresponded to APA and 3 to PC. No differences were observed in the expression of PGP 9.5 (P=0.5) or galectin-3 (P=0.7) between PC and APA. The group of tumours not expressing parafibromin were associated with age (74±13.3 vs 54.36±16.3 years, P=0.04), higher frequency of bone fractures (40% (n=2/5) vs 0% (n=0/12), P=0.07), capsular invasion (100% (n=5/5) vs 58.3% (n=7/12), P=0.06), infiltration of adjacent structures (100% (n=5/5) vs 33.3% (n=4/12), P=0.05) and loss of PGP 9.5 expression (80% (n=4/5) vs 16.7% (n=2/12), P=0.02).

Conclusion: No analytical or clinical behavioural differences were observed between PCs and APAs. Interestingly, loss of parafibromin is associated with locally more aggressive tumour behaviour.