Diagnostic and prognostic implications of parafibromin immunohistochemistry in parathyroid carcinomaT

Para This, Fibromin That: The Role of CDC73 in Parathyroid Tumors and Familial Tumor Syndromes

CDC73 alterations are associated with three main parathyroid lesions according to the World Health Organization (WHO) classification of tumors of the endocrine system. These include hyperparathyroidism-jaw tumor (HPT-JT) syndrome-associated adenomas, atypical parathyroid tumors (APTs), and parathyroid carcinomas (PCs). The loss of nuclear parafibromin expression, which serves as a surrogate marker for the underlying CDC73 alteration, encompasses these tumors under the term parafibromin-deficient parathyroid tumors. They have distinct morphologic features of more abundant eosinophilic cytoplasm with perinuclear clearing surrounding a large nucleus as well as prominent dilated branching "hemangiopericytoma-like" vasculature and a thick capsule as well as variably sized cystic spaces. These tumors include cases that show unequivocal histologic features fulfilling the criteria for PCs with growing data indicating a higher rate of recurrence or metastasis compared with parafibromin intact PCs. More importantly, the loss of parafibromin expression can be used in clinical practice to recognize APTs that fall short of a conclusive diagnosis of PCs, but clinically behave akin to them. Moreover, recognizing these tumors can lead to an underlying germline mutation and a diagnosis of HPT-JT, which impacts long-term treatment and surveillance for patients and close family.

Preoperative, Intraoperative, and Postoperative Parathyroid Pathology: Clinical Pathologic Collaboration for Optimal Patient Management

Parathyroid disease typically presents with parathyroid hyperfunction as result of neoplasia or a consequence of non-neoplastic systemic disease. Given the parathyroid gland is a hormonally active organ with broad physiologic implications and serologically accessible markers for monitoring, the diagnosis of parathyroid disease is predominantly a clinical pathologic correlation. We provide the current pathological correlates of parathyroid disease and discuss preoperative, intraoperative, and postoperative pathology consultative practice for optimal patient care.

The roles of the tumor suppressor parafibromin in cancer

In this review, we discuss parafibromin protein, which is encoded by CDC73. A mutation in this gene causes hyperparathyroidism-jaw tumor (HPT-JT) syndrome, an autosomal dominant disease. CDC73 is transcriptionally downregulated by the Wilms’ tumor suppressor gene WT1 and translationally targeted by miR-182-3p and miR-155. In the nucleus, parafibromin binds to RNA polymerase II and PAF1 complex for transcription. Parafibromin transcriptionally increases the expression of c-Myc, decreases CPEB1 expression by interacting with H3M4, and reduces cyclin D1 expression by binding to H3K9. The RNF20/RNF40/parafibromin complex induces monoubiquitination of H2B-K120, and SHP2-mediated dephosphorylation of parafibromin promotes the parafibromin/β-catenin interaction and induces the expression of Wnt target genes, which is blocked by PTK6-medidated phosphorylation. Parafibromin physically associates with the CPSF and CstF complexes that are essential for INTS6 mRNA maturation. In the cytosol, parafibromin binds to hSki8 and eEF1Bγ for the destabilization of p53 mRNA, to JAK1/2-STAT1 for STAT1 phosphorylation, and to actinin-2/3 to bundle/cross-link actin filaments. Mice with CDC73 knockout in the parathyroid develop parathyroid and uterine tumors and are used as a model for HPT-JT syndrome. Conditional deletion of CDC73 in mesenchymal progenitors results in embryos with agenesis of the heart and liver while its abrogation in mature osteoblasts and osteocytes increases cortical and trabecular bone. Heterozygous germline mutations in CDC73 are associated with parathyroid carcinogenesis. The rates of CDC73 mutation and parafibromin loss decrease from parathyroid adenoma to atypical adenoma to carcinoma. In addition, down-regulated parafibromin is closely linked to the tumorigenesis, subsequent progression, or poor prognosis of head and neck, gastric, lung, colorectal, and ovarian cancers, and its overexpression might reverse the aggressiveness of these cancer cells. Therefore, parafibromin might be useful as a biological marker of malignancies and a target for their gene therapy.

Parathyroid Carcinoma and Ectopic Secretion of Parathyroid hormone

The most common causes of hypercalcemia are primary hyperparathyroidism (PHPT) and malignancy. Parathyroid carcinoma (PC), causing a severe PHPT, is the rarest parathyroid tumor. A diagnosis of PC is challenging because the clinical profile overlaps with that of benign counterpart. Surgery is the mainstay treatment. CDC73 mutations have been detected in up to 80% of sporadic PCs. Ectopic production of parathyroid hormone (PTH) by malignant nonparathyroid tumors is a rare condition accounting for less than 1% of hypercalcemia of malignancy. PTH secretion can be considered an aberration in the tissue specificity of gene expression and may involve heterogeneous molecular mechanisms.

Genomics and Epigenomics in Parathyroid Neoplasia: from Bench to Surgical Pathology Practice

The majority of parathyroid disease encountered in routine practice is due to single parathyroid adenoma, of which the majority arise as sporadic tumors. This is usually a straightforward diagnosis in endocrine pathology when in the appropriate clinical setting, although subsets of cases will exhibit atypical histological features that may warrant additional immunohistochemical and genetic analyses to estimate the malignant potential. Parathyroid carcinomas on the other hand, are bona fide malignant tumors characterized by their unequivocal invasion demonstrated through routine histology or metastasis. The ultimate endpoint for any molecular marker discovered through laboratory investigations is to be introduced in clinical routine practice and guide the surgical pathologist in terms of diagnostics and prognostication. For parathyroid tumors, the two main diagnostic challenges include the distinction between parathyroid adenoma and parathyroid carcinoma, as well as the pinpointing of hereditable disease for familial screening purposes. While numerous markers on genetic, epigenetic, and protein levels have been proposed as discriminative in these aspects, this review aims to condense the scientific coverage of these enigmatic topics and to propose a focused surgical pathology approach to the subject.

Histone Monoubiquitination in Chromatin Remodelling: Focus on the Histone H2B Interactome and Cancer

Chromatin remodelling is a major mechanism by which cells control fundamental processes including gene expression, the DNA damage response (DDR) and ensuring the genomic plasticity required by stem cells to enable differentiation. The post-translational modification of histone H2B resulting in addition of a single ubiquitin, in humans at lysine 120 (K120; H2Bub1) and in yeast at K123, has key roles in transcriptional elongation associated with the RNA polymerase II-associated factor 1 complex (PAF1C) and in the DDR. H2Bub1 itself has been described as having tumour suppressive roles and a number of cancer-related proteins and/or complexes are recognised as part of the H2Bub1 interactome. These include the RING finger E3 ubiquitin ligases RNF20, RNF40 and BRCA1, the guardian of the genome p53, the PAF1C member CDC73, subunits of the switch/sucrose non-fermenting (SWI/SNF) chromatin remodelling complex and histone methyltransferase complexes DOT1L and COMPASS, as well as multiple deubiquitinases including USP22 and USP44. While globally depleted in many primary human malignancies, including breast, lung and colorectal cancer, H2Bub1 is selectively enriched at the coding region of certain highly expressed genes, including at p53 target genes in response to DNA damage, functioning to exercise transcriptional control of these loci. This review draws together extensive literature to cement a significant role for H2Bub1 in a range of human malignancies and discusses the interplay between key cancer-related proteins and H2Bub1-associated chromatin remodelling.

Clinical Presentation, Treatment, and Outcome of Parathyroid Carcinoma: Results of the NEKAR Retrospective International Multicenter Study

OBJECTIVE

In this retrospective cohort study, we describe the clinical presentation and workup of parathyroid carcinoma (PC) and determine its clinical prognostic parameters. Primary outcome was recurrence free survival.

SUMMARY BACKGROUND DATA

PC is an orphan malignancy for which diagnostic workup and treatment is not established.

METHODS

Eighty-three patients were diagnosed with PC between 1986 and 2018. Disease-specific and recurrence-free survivals were estimated with the Kaplan-Meier method. Risk factors for recurrence were identified by binary logistic regression with adjustment for age and sex. Thirty-nine tumors underwent central histopathological review.

RESULTS

Renal (39.8%), gastrointestinal (24.1%), bone (22.9%), and psychiatric (19.3%) symptoms were the most common symptoms. Surgical treatment was heterogeneous [parathyroidectomy [PTx)] alone: 22.9%; PTx and hemithyroidectomy: 24.1%; en bloc resection 15.7%; others 37.3%] and complications of surgery were frequent (recurrent laryngeal nerve palsy 25.3%; hypoparathyroidism 6%). Recurrence of PC was observed in 32 of 83 cases. In univariate analysis, rate of recurrence was reduced when extended initial surgery had been performed (P = 0.04). In multivariate analysis low T status [odds ratio (OR) = 2.65, 95% confidence interval (CI) 1.02-6.88, P = 0.045], N0 stage at initial diagnosis (OR = 6.32, 95% CI 1.33-30.01, P = 0.02), Ki-67 <10% (OR = 14.07, 95% CI 2.09-94.9, P = 0.007), and postoperative biochemical remission (OR = 0.023, 95% CI 0.001-0.52, P = 0.018) were beneficial prognostic parameters for recurrence-free survival.

CONCLUSION

Despite a favorable overall prognosis, PC shows high rates of recurrence leading to repeated surgery and postoperative recurrent laryngeal nerve palsy and hypoparathyroidism. In view of the reduced recurrence rate in cases of extended surgery, ipsilateral completion surgery may be considered when PC is confirmed.