Genetic Alteration Profiles and Clinicopathological Associations in Atypical Parathyroid Adenoma

Somatic and Germline Mutations in Atypical Parathyroid Tumors

This case series examines somatic and germline mutations in atypical parathyroid adenomas using broad next-generation sequencing of tumor samples obtained from patients who underwent surgical resection from 2020 to 2022.

Patterns and Predictors of Cervical Lymph Node Metastasis in Parathyroid Carcinoma

Simple Summary

Parathyroid carcinoma (PC) is a rare endocrine malignancy with poor outcomes. Surgery remains the mainstay of PC treatment. However, due to the rarity of this malignancy, the optimal extent of PC surgery remains inconclusive, including whether to perform central lymph node dissection (LND). In the present study, we reported the patterns and predictors of cervical lymph node metastasis in PC based on a cohort of 68 PC patients. The results showed that the percentage of cervical lymph node metastasis in PC was 19.4% at initial surgery and 25.0% including reoperations for recurrencies. High-risk Schulte staging and CDC73 abnormalities were identified as risk factors for cervical lymph node metastasis. Central LND should be considered during remedial surgeries performed after previous local resection of PC for patients with high risk factors.

Abstract

Background: Parathyroid carcinoma (PC) is a rare endocrine malignancy with poor outcomes. Over 60% of PC patients experience repeated disease recurrence or metastasis. The significance of cervical lymph node dissection (LND) for PC remains inconclusive. Methods: PC patients diagnosed at Peking Union Medical College Hospital between 1992 and 2021 were reviewed retrospectively. Clinical data, initial tumor histological staging, parafibromin histochemical staining results, Ki67 index, CDC73 gene mutation status and outcome information were collected systemically. The risk factors for recurrence and lymph node or distant metastasis were explored. Results: Sixty-eight PC patients receiving LND were enrolled. Cervical lymph node metastasis was identified in 19.4% of patients at initial surgery and 25.0% of patients including reoperations for recurrences. The independent risk factor for PC recurrence was a Ki67 index ≥ 5% (HR4.41, 95% confidence interval (CI)1.30–14.95, p = 0.017). Distant metastasis was an independent prognostic factor for PC patient overall survival (HR 5.44, 95% CI 1.66–17.82, p = 0.005). High-risk Schulte staging (p = 0.021) and CDC73 abnormalities (p = 0.012) were risk factors for cervical lymph node metastasis. Conclusion: Most PCs were slow-growing, but lymph node metastasis was not rare. For patients planning to undergo remedial surgery after previous local resection of PC, central LND is suggested for tumors with high-risk Schulte staging or CDC73 abnormalities.

Parathyroid Crisis as Presentation of Atypical Parathyroid Adenoma: Two Diagnostically Challenging Cases

Atypical parathyroid adenoma (APA) is a rare cause of primary hyperparathyroidism (PHPT) and represents a diagnostic challenge since it is an intermediate form of parathyroid neoplasm of uncertain malignant potential with atypical histological features that require differential diagnosis of parathyroid carcinoma (PC). We present 2 cases of parathyroid crisis as a presentation of APA. The first case was that of a 56-year-old man with parathyroid crisis, constitutional syndrome, and anemia, with evidence of APA after en bloc resection, evolving with hungry bone syndrome after surgery and curation criteria at 6 months after parathyroidectomy (PTX). The second case was a 64-year-old woman with acute chronic kidney disease and parathyroid crisis, with evidence of APA after selective PTX and >50% reduction in parathyroid hormone levels after surgery; however, persistent PHPT at 6 months post-surgery was observed. These cases represented a diagnostic challenge due to their rare clinical presentation (parathyroid crisis), with a heterogeneous spectrum of target organ damage and infrequent symptoms (constitutional syndrome and acute chronic renal disease), in turn caused by a rare pathology (APA). The presentation of these patients may be indicative of PC; however, histopathological diagnosis is a key to the diagnosis of APA. The differential diagnosis of APA vs. PC in clinical practice is indispensable.

Overview of the 2022 WHO Classification of Parathyroid Tumors

The 2022 WHO classification reflects increases in the knowledge of the underlying pathogenesis of parathyroid disease. In addition to the classic characteristic features of parathyroid neoplasms, subtleties in histologic features which may indicate an underlying genetic abnormality reflect increased understanding of the clinical manifestations, histologic, and genetic correlation in parathyroid disease. The importance of underlying genetic aberrancies is emphasized due to their significance to the care of the patient. Traditionally, the term "parathyroid hyperplasia" has been applied to multiglandular parathyroid disease; however, the concept of hyperplasia is generally no longer supported in the context of primary hyperparathyroidism since affected glands are usually composed of multiple "clonal" neoplastic proliferations. In light of these findings and management implications for patient care, the 2022 WHO classification endorses primary hyperparathyroidism-related multiglandular parathyroid disease (multiglandular multiple parathyroid adenomas) as a germline susceptibility-driven multiglandular parathyroid neoplasia. From such a perspective, pathologists can provide additional value to genetic triaging by recognizing morphological and immunohistochemical harbingers of MEN1, CDKN1B, MAX, and CDC73-related manifestations. In the current WHO classification, the term "parathyroid hyperplasia" is now used primarily in the setting of secondary hyperplasia which is most often caused by chronic renal failure. In addition to expansion in the histological features, including those that may be suggestive of an underlying genetic abnormality, there are additional nomenclature changes in the 2022 WHO classification reflecting increased understanding of the underlying pathogenesis of parathyroid disease. The new classification no longer endorses the use of "atypical parathyroid adenoma". This entity is now being replaced with the term of "atypical parathyroid tumor" to reflect a parathyroid neoplasm of uncertain malignant potential. The differential diagnoses of atypical parathyroid tumor are discussed along with the details of worrisome clinical and laboratory findings, and also features that define atypical histological and immunohistochemical findings to qualify for this diagnosis. The histological definition of parathyroid carcinoma still requires one of the following findings: (i) angioinvasion (vascular invasion) characterized by tumor invading through a vessel wall and associated thrombus, or intravascular tumor cells admixed with thrombus, (ii) lymphatic invasion, (iii) perineural (intraneural) invasion, (iv) local malignant invasion into adjacent anatomic structures, or (v) histologically/cytologically documented metastatic disease. In parathyroid carcinomas, the documentation of mitotic activity (e.g., mitoses per 10mm²) and Ki67 labeling index is recommended. Furthermore, the importance of complete submission of parathyroidectomy specimens for microscopic examination, and the crucial role of multiple levels along with ancillary biomarkers have expanded the diagnostic workup of atypical parathyroid tumors and parathyroid carcinoma to ensure accurate characterization of parathyroid neoplasms. The concept of parafibromin deficiency has been expanded upon and term "parafibromin deficient parathyroid neoplasm" is applied to a parathyroid neoplasm showing complete absence of nuclear parafibromin immunoreactivity. Nucleolar loss is considered as abnormal finding that requires further molecular testing to confirm its biological significance. The 2022 WHO classification emphasizes the role of molecular immunohistochemistry in parathyroid disease. By adopting a question-answer framework, this review highlights advances in knowledge of histological features, ancillary studies, and associated genetic findings that increase the understanding of the underlying pathogenesis of parathyroid disease that are now reflected in the updated classification and new entities in the 2022 WHO classification.