Endocrine Abstracts

Background: Atypical parathyroid tumor (APT) generally has a better prognosis compared to parathyroid carcinoma (PC). The differential diagnosis of APT and PC is crucial for further management. Diagnosis of both is based on morphological examination but sometimes can be challenging. In such cases immunohistochemistry (IHC) should be used.

Objective: To estimate the utility of IHC in the differential diagnosis of APT and PC.

Materials and Methods: We conducted a single-centre retrospective study of 44 patients with morphological diagnosis “;APT”; who underwent parathyroidectomy between 2018 and 2023. Method of sampling was continuous. The research complied with the principles of the Helsinki Declaration. IHC was performed in all cases: assessment of CD31/CD34 (to identify vascular invasion), parathyroid hormone (PTH) and parafibromin expression; Ki-67 evaluation. According to IHC results patients were divided into 2 groups: APT and PC followed by comparative analysis. This analysis included biochemical markers of Ca-P metabolism (Сa adj., P, PTH, eGFR CKD-EPI, ALP, osteocalcin, CT×); the frequency of “;classic”; PHPT complications and intraoperative signs of surrounding tissue invasion; size and volume of tumor according to US; morphological features of uncertain malignant potential. Comparison of two independent groups for quantitative data was performed using the Mann–Whitney test (U-test), the frequencies of binary variables using the two-tailed Fisher exact test. The Bonferroni correction was applied by correcting the significance threshold (P=0.002).

Results: Based on the IHC results in 8/44 patients (18.2%) the diagnosis was reclassified as PC. In 7/8 (87.5%) vascular invasion was identified by CD31/CD34 expression (endothelial markers). In 1/8 (12.5%) additional sections revealed a foci of the tumor growth detected with PTH expression in the surrounding fatty tissue. PC and APT groups were comparable for high values of PHT, Ca adj. and 24-h urinary Ca excretion, the frequency of bone and kidney disorders. Moreover, there was no difference in morphological features of uncertain malignant potential. Statistically significant trend was defined only for the frequency of pathological mitosis (more typical in patients with PC). Ki-67% and parafibromin expression also did not differ between groups.

Conclusion: Evaluation of preoperative clinical and laboratory-instrumental data does not allow to differentiate APT and PC. If APT is morphologically suspected, IHC is strongly recommended to exclude PC.