CDC73 Mutation Research Articles

Parathyroid carcinoma: molecular pathology and correlation with clinicopathologic features, a single center experience

Abstract Introduction/Objective Parathyroid Carcinomas are rare malignant neoplasms, accounting for less than 1% of primary hyperparathyroidism cases. Parathyroid carcinomas are characterized by markedly elevated levels of PTH, severe hypercalcemia and established target organ damage. The authors report the experience of a single center regarding the clinic-pathologic and genetic analysis of parathyroid carcinoma cases. Methods/Case Report The study is a retrospective review of all patients with parathyroid carcinoma that were evaluated at a tertiary oncologic center from 2001 until 2023. Results (if a Case Study enter NA) A total of nine cases (6 male and 3 female) were identified, with a mean age at diagnosis of 52 ± 16 years and a median follow-up of 16.5 years. Most patients presented with hypercalcemia (n = 7), with a mean serum calcium concentration of 13.5 mg/dl (9.6-16.5) and a mean PTH of 1123 pg/ml (<a href=“tel:276- 2500”>276-2500</a>). En bloc surgical resection was performed in 6 patients and 3 patients underwent adjuvant radiotherapy. Recurrence was observed in 4 cases (44.4%) after a median of 24 months following surgery. Negative immunohistochemical staining of parafibromin was noted in 3/4 cases of recurrence. Parathyroid carcinoma was diagnosed on the basis of finding lesions with vascular or perineural invasion, capsular penetration, and/or documented metastases. Immunohistochemical staining for parafibromin, Ki-67, and E-cadherin was performed on formalin-fixed, paraffin-embedded tissue samples. Next generation sequencing (NGS) was performed in 6/9 cases and CDC73 mutations were present in 38.5% of analyzed patients. Loss of TP53 and RB1 alleles and CCND1 amplification were other reported genetic alterations in the study cohort. Conclusion Parathyroid carcinoma is associated with a significant rate of recurrence and limited effective treatment beyond initial complete surgical resection. Inactivating CDC73 alterations which include truncating or frameshift mutations, as well as missense mutations lead to the loss of parafibromin immunoreactivity. Other molecular alterations like PTEN and PIK3CA mutations may represent potential targets for molecular therapy. An IHC panel of parafibromin, Ki-67 and E-cadherin may help to distinguish parathyroid carcinoma from other parathyroid neoplasms.

7508 Primary Hyperparathyroidism Caused By A CDC73-related Atypical Parathyroid Tumor

Abstract Disclosure: R. Cardenas: None. S. Tariq: None. R. Habibi: None. N. Ebrahimi: None. E. Astiazaran-Symonds: None. Background: Primary hyperparathyroidism (PHPT) is a common endocrine disease, causes include: parathyroid adenomas (80-85%), parathyroid hyperplasia (10-15%), atypical parathyroid adenomas (APA) (1.2 %) and parathyroid carcinomas (PC) (1%). APA share many anatomic and histopathologic features with PC making the distinction between the two challenging. Although most are sporadic, some APA are caused by germline mutations in the CDC73 gene, which is associated with hyperparathyroidism-jaw tumor (HPT-JT) syndrome PC and familial isolated PHPT with APA. Clinical Case: A 42-year-old female presented to the clinic for evaluation of recurrent PHPT. She was diagnosed at age 22 when she experienced fatigue, polydipsia with hypercalcemia (12.9mg/dl). She underwent superior bilateral parathyroidectomy with pathology consistent with parathyroid adenoma. Twenty years later, symptoms recurred and tests showed hypercalcemia (13.0 mg/dl), elevated PTH (252 pg/dl), kidney function preserved (GFR: 82.5 ml/min), normal vitamin D 25 OH (31 ng/dl). Patient denied history of nephrolithiasis or fractures. Family history was positive for kidney stones in father and siblings, also history of a jaw tumor in niece. Sestamibi scan showed a left inferior parathyroid adenoma. Patient underwent resection of the adenoma; pathology revealed a left parathyroid adenoma with atypical parathyroid tumor, >95% cellularity with cytologic features concerning for malignancy, prominent macronucleoli, necrosis, elevated mitotic activity and Ki67 with 15% tumor cells without vascular invasion. Post-op Calcium and PTH normalized (9.6 mg/dl and 10.8 pg/ml, respectively). Genetic testing via multi-gene panel identified a whole gene deletion of CDC73, consistent with hyperparathyroidism-jaw tumor syndrome. Panoramic jaw x-rays did not show jaw tumors. Genetic testing for family members is underway. Conclusion: Although somatic mutations in CDC73 are frequently found in sporadic APA and PC, germline mutations are a rare cause of PHPT associated with these tumors. Histopathological examination is necessary to confirm the diagnosis of APA and to differentiate it from PC, which has a recurrence rate >50%. APA should be treated as a “tumor of uncertain malignant potential” and needs to be carefully and periodically followed up with measurement of Ca, PTH and vitamin D. Confirmation of a CDC73 mutation by genetic testing helped identify the increased risk for other associated tumors in jaw, kidneys and uterus prompting initiation of surveillance with panoramic jaw x-rays with neck shielding, renal US and pelvis US. Genetic testing of family members will allow timely detection and treatment of individuals at risk. Presentation: 6/3/2024

12312 A Comparative Genomic Analysis Between Parathyroid Adenomas And Carcinomas With Heterozygous Germline Cdc73 Mutations

Abstract Disclosure: Y. Li: None. W.F. Simonds: None. H. Chen: None. Introduction: Parathyroid cancer is responsible for ∼1% of primary hyperparathyroidism. The hereditary form of this malignancy has been linked to germline mutations of the CDC73 gene. We previously reported that only the germline CDC73 mutations causing a significant impact on the function/expression of its encoded protein are associated with parathyroid carcinomas. On the other hand, these germline mutations may lead to only parathyroid adenomas or no parathyroid disease, suggesting incomplete penetrance. This observation raises the question of what additional genomic events are required for parathyroid tumorigenesis in carriers with germline CDC73 mutations. Methods: Twelve patients harboring heterozygous germline CDC73 mutations were included in this study. Whole exome sequencing was performed in all 12 parathyroid tumors (6 adenomas and 6 carcinomas) and the paired normal tissues. RNA sequencing was successfully performed in three of each parathyroid carcinomas, adenomas, and normal glands. The sequencing raw data were processed using the CCBR-Pipeliner. EnrichR, Gene Set Enrichment Analysis, and CIBERSORT were used for the downstream analyses. Results: All parathyroid carcinomas and adenomas had gained one somatic event predicted to cause a complete inactivation of the second CDC73 allele. Several distinctive genomic features were identified in parathyroid carcinomas compared to adenomas, including more single nucleotide variants bearing the signature of APOBEC deamination, frequent mutations among the genes involved in the PI-3K/mTOR signaling, and substantially more copy number variations and differentially expressed genes. Parathyroid carcinomas also share some genomic features with adenomas. For instance, both tumors have frequent somatic mutations and copy number loss that impact the genes related to T-cell receptor signaling and tumor antigen presentation, suggesting a shared strategy to evade immune surveillance. Consistent with these findings, an in silico estimation of immune cell composition in tumors found an absence of CD8+ T-cells in parathyroid adenomas and carcinomas. Conclusion: Our study provides evidence that biallelic inactivation of CDC73 is essential for parathyroid tumorigenesis in carriers with germline mutations of this gene. Despite sharing some genomic features with adenomas, parathyroid carcinomas have more distinctive alterations in the genome, some of which may be critical for cancer formation. Presentation: 6/2/2024

8592 Parathyroid Carcinoma: A Rare Cause of Primary Hyperparathyroidism

Abstract Disclosure: S.E. Koshy: None. C.F. Mulcahy: None. P.S. Kothari: None. E.M. Jacobi: None. T.D. Cubb: None. Introduction: Parathyroid carcinoma (PC) is a rare malignancy that accounts for <1% of cases of primary hyperparathyroidism (PHPT). Patients often present with symptoms of hypercalcemia, serum calcium (Ca) >14 mg/dL, large tumor size, and a very high parathyroid hormone (PTH) level. We report a case of an asymptomatic patient with incidentally found hypercalcemia consistent with PHPT who was ultimately diagnosed with PC. Clinical Case: A 31yo male was found to have elevated serum Ca of 12.7 mg/dL (8.6-10.3 mg/dL) on labs obtained during routine physical exam. He had no known significant medical or family history and notably had no laboratory evaluation within the prior 10 years. He denied constipation, polyuria, confusion, depression, bone pain, and history of fractures or nephrolithiasis. Workup showed an inappropriately elevated PTH of 505 pg/mL (16-77 pg/mL). Neck ultrasound demonstrated a left inferior 3.9 cm complex thyroid nodule. Sestamibi scan confirmed increased uptake in the inferior left thyroid. Left neck exploration was performed. Intraoperatively, a 3.7 cm left parathyroid mass weighing 13.0 grams was encountered and excised in an en bloc fashion. The left superior parathyroid gland was evaluated and found to be normal. Intraoperative PTH level decreased from 529 pg/mL to 48 pg/mL 10 minutes after excision. Left hemithyroidectomy was not performed. Surgical pathology revealed PC with lymphovascular invasion, suspected capsular invasion, and negative margins. Immunohistochemical staining showed a Ki67 proliferation index up to 5% and complete loss of nuclear staining for parafibromin. Next generation sequencing demonstrated a somatic CDC73 p.L8fs mutation, tumor mutational burden 4.7m/MB, and stable microsatellite instability. Germline testing was negative for a CDC73 mutation. Postoperative staging did not demonstrate evidence of metastatic disease in the neck or chest. Serum Ca remained within normal limits. After multidisciplinary discussion, no further surgical intervention was recommended and plan was for ongoing biochemical and imaging surveillance. Conclusion: Though rare, PC should be considered as a cause of PHPT. The primary treatment is complete surgical resection. Unfortunately, there is a high rate of recurrence, >50%, with most occurring 2-5 years after initial surgery with a median overall survival of 14 years. Thus, long-term surveillance is of utmost importance. Treatment of recurrent disease is surgical resection when feasible as well as medical management of hypercalcemia. Further research is needed to better understand the role of targeted systemic therapy in addition to immunotherapy. PC is most commonly sporadic but can be hereditary, thus genetic evaluation is recommended. Given its rarity and complexity, PC is best managed in a multidisciplinary setting. Presentation: 6/1/2024

12312 A Comparative Genomic Analysis Between Parathyroid Adenomas And Carcinomas With Heterozygous Germline Cdc73 Mutations

Abstract Disclosure: Y. Li: None. W.F. Simonds: None. H. Chen: None. Introduction: Parathyroid cancer is responsible for ∼1% of primary hyperparathyroidism. The hereditary form of this malignancy has been linked to germline mutations of the CDC73 gene. We previously reported that only the germline CDC73 mutations causing a significant impact on the function/expression of its encoded protein are associated with parathyroid carcinomas. On the other hand, these germline mutations may lead to only parathyroid adenomas or no parathyroid disease, suggesting incomplete penetrance. This observation raises the question of what additional genomic events are required for parathyroid tumorigenesis in carriers with germline CDC73 mutations. Methods: Twelve patients harboring heterozygous germline CDC73 mutations were included in this study. Whole exome sequencing was performed in all 12 parathyroid tumors (6 adenomas and 6 carcinomas) and the paired normal tissues. RNA sequencing was successfully performed in three of each parathyroid carcinomas, adenomas, and normal glands. The sequencing raw data were processed using the CCBR-Pipeliner. EnrichR, Gene Set Enrichment Analysis, and CIBERSORT were used for the downstream analyses. Results: All parathyroid carcinomas and adenomas had gained one somatic event predicted to cause a complete inactivation of the second CDC73 allele. Several distinctive genomic features were identified in parathyroid carcinomas compared to adenomas, including more single nucleotide variants bearing the signature of APOBEC deamination, frequent mutations among the genes involved in the PI-3K/mTOR signaling, and substantially more copy number variations and differentially expressed genes. Parathyroid carcinomas also share some genomic features with adenomas. For instance, both tumors have frequent somatic mutations and copy number loss that impact the genes related to T-cell receptor signaling and tumor antigen presentation, suggesting a shared strategy to evade immune surveillance. Consistent with these findings, an in silico estimation of immune cell composition in tumors found an absence of CD8+ T-cells in parathyroid adenomas and carcinomas. Conclusion: Our study provides evidence that biallelic inactivation of CDC73 is essential for parathyroid tumorigenesis in carriers with germline mutations of this gene. Despite sharing some genomic features with adenomas, parathyroid carcinomas have more distinctive alterations in the genome, some of which may be critical for cancer formation. Presentation: 6/2/2024

8592 Parathyroid Carcinoma: A Rare Cause of Primary Hyperparathyroidism

Abstract Disclosure: S.E. Koshy: None. C.F. Mulcahy: None. P.S. Kothari: None. E.M. Jacobi: None. T.D. Cubb: None. Introduction: Parathyroid carcinoma (PC) is a rare malignancy that accounts for <1% of cases of primary hyperparathyroidism (PHPT). Patients often present with symptoms of hypercalcemia, serum calcium (Ca) >14 mg/dL, large tumor size, and a very high parathyroid hormone (PTH) level. We report a case of an asymptomatic patient with incidentally found hypercalcemia consistent with PHPT who was ultimately diagnosed with PC. Clinical Case: A 31yo male was found to have elevated serum Ca of 12.7 mg/dL (8.6-10.3 mg/dL) on labs obtained during routine physical exam. He had no known significant medical or family history and notably had no laboratory evaluation within the prior 10 years. He denied constipation, polyuria, confusion, depression, bone pain, and history of fractures or nephrolithiasis. Workup showed an inappropriately elevated PTH of 505 pg/mL (16-77 pg/mL). Neck ultrasound demonstrated a left inferior 3.9 cm complex thyroid nodule. Sestamibi scan confirmed increased uptake in the inferior left thyroid. Left neck exploration was performed. Intraoperatively, a 3.7 cm left parathyroid mass weighing 13.0 grams was encountered and excised in an en bloc fashion. The left superior parathyroid gland was evaluated and found to be normal. Intraoperative PTH level decreased from 529 pg/mL to 48 pg/mL 10 minutes after excision. Left hemithyroidectomy was not performed. Surgical pathology revealed PC with lymphovascular invasion, suspected capsular invasion, and negative margins. Immunohistochemical staining showed a Ki67 proliferation index up to 5% and complete loss of nuclear staining for parafibromin. Next generation sequencing demonstrated a somatic CDC73 p.L8fs mutation, tumor mutational burden 4.7m/MB, and stable microsatellite instability. Germline testing was negative for a CDC73 mutation. Postoperative staging did not demonstrate evidence of metastatic disease in the neck or chest. Serum Ca remained within normal limits. After multidisciplinary discussion, no further surgical intervention was recommended and plan was for ongoing biochemical and imaging surveillance. Conclusion: Though rare, PC should be considered as a cause of PHPT. The primary treatment is complete surgical resection. Unfortunately, there is a high rate of recurrence, >50%, with most occurring 2-5 years after initial surgery with a median overall survival of 14 years. Thus, long-term surveillance is of utmost importance. Treatment of recurrent disease is surgical resection when feasible as well as medical management of hypercalcemia. Further research is needed to better understand the role of targeted systemic therapy in addition to immunotherapy. PC is most commonly sporadic but can be hereditary, thus genetic evaluation is recommended. Given its rarity and complexity, PC is best managed in a multidisciplinary setting. Presentation: 6/1/2024

A Comparative Genomic Analysis of Parathyroid Adenomas and Carcinomas Harboring Heterozygous Germline CDC73 Mutations.

Parathyroid cancer has been linked to germline mutations of the CDC73 gene. However, carriers harboring cancer-associated germline CDC73 mutations may develop only parathyroid adenoma or no parathyroid disease. This incomplete penetrance indicates that additional genomic events are required for parathyroid tumorigenesis. (1) Determine the status of the second CDC73 allele in parathyroid tumors harboring germline CDC73 mutations, and (2) compare the genomic landscapes between parathyroid carcinomas and adenomas. Whole-exome and RNA sequencing of 12 parathyroid tumors harboring germline CDC73 mutations (6 adenomas and 6 carcinomas) and their matched normal tissues. All 12 parathyroid tumors had gained one somatic event predicted to cause a complete inactivation of the second CDC73 allele. Several distinctive genomic features were identified in parathyroid carcinomas compared to adenomas, including more single nucleotide variants bearing the C>G transversion and APOBEC deamination signatures, frequent mutations of the genes involved in the PI-3K/mTOR signaling, a greater number of copy number variations, and substantially more genes with altered expression. Parathyroid carcinomas also share some genomic features with adenomas. For instance, both have recurrent somatic mutations and copy number loss that impact the genes involved in T-cell receptor signaling and tumor antigen presentation, suggesting a shared strategy to evade immune surveillance. Biallelic inactivation of CDC73 is essential for parathyroid tumorigenesis in carriers harboring germline mutations of this gene. Despite sharing some genomic features with adenomas, parathyroid carcinomas have more distinctive alterations in the genome, some of which may be critical for cancer formation.

Whole-exome Sequencing of Atypical Parathyroid Tumors Detects Novel and Common Genes Linked to Parathyroid Tumorigenesis

Abstract Context Atypical parathyroid tumor (APT) represents a neoplasm characterized by histological features typical of parathyroid carcinoma (PC) but lacking local infiltration and/or distant metastasis, leading to uncertainty regarding its malignant potential. Objective To characterize the molecular landscape and deregulated pathways in APT. Methods Whole-exome sequencing (WES) was conducted on 16 APTs. DNA from tumors and matched peripheral blood underwent WES using Illumina HiSeq3000. Results A total of 192 nonsynonymous variants were identified. The median number of protein-altering mutations was 9. The most frequently mutated genes included BCOR, CLMN, EZH1, JAM2, KRTAP13-3, MUC16, MUC19, and OR1S1. Seventeen mutated genes belong to the Cancer Gene Census list. The most consistent hub genes identified through STRING network analysis were ATM, COL4A5, EZH2, MED12, MEN1, MTOR, PI3, PIK3CA, PIK3CB, and UBR5. Deregulated pathways included the PI3 K/AKT/mTOR pathway, Wnt signaling, and extracellular matrix organization. Variants in genes such as MEN1, CDC73, EZH2, PIK3CA, and MTOR, previously reported as established or putative/candidate driver genes in benign adenoma (PA) and/or PC, were also identified in APT. Conclusion APT does not appear to have a specific molecular signature but shares genomic alterations with both PA and PC. The incidence of CDC73 mutations is low, and it remains unclear whether these mutations are associated with a higher risk of recurrence. Our study confirms that PI3 K/AKT/mTOR and Wnt signaling represents the pivotal pathways in parathyroid tumorigenesis and also revealed mutations in key epigenetic modifier genes (BCOR, KDM2A, MBD4, and EZH2) involved in chromatin remodeling, DNA, and histone methylation.

Insights into Hyperparathyroidism-Jaw Tumour Syndrome: From Endocrine Acumen to the Spectrum of CDC73 Gene and Parafibromin-Deficient Tumours.

A total of 1 out of 10 patients with primary hyperparathyroidism (PHP) presents an underlying genetic form, such as multiple endocrine neoplasia types 1, 2A, etc., as well as hyperparathyroidism-jaw tumour syndrome (HJT). We aimed to summarise the recent data, thus raising more awareness regarding HJT, from the clinical perspective of PHP in association with the challenges and pitfalls of CDC73 genetic testing and parafibromin staining. This narrative review included a sample-focused analysis from the past decade according to a PubMed search. We identified 17 original human studies (≥4 patients per article). The mean age at disease onset was between 20.8 and 39.5 years, while the largest study found that 71% of patients had HJT recognised before the age of 30. Males and females seemed to be equally affected, in contrast with sporadic PHP. PHP represented the central manifestation of HJT, occurring as the first manifestation in up to 85% of HJT cases. A biochemistry panel found a mean serum calcium level above the level of 12 mg/dL in PHP. PTH was elevated in HJT as well, with average values of at least 236.6 pg/mL. The most frequent pathological type in PHP was a parathyroid adenoma, but the incidence of a parathyroid carcinoma was much higher than in non-HJT cases (15% of all parathyroid tumours), with the diagnosis being established between the age of 15 and 37.5. In some families up to 85% of carriers suffered from a parathyroid carcinoma thus indicating that certain CDC73 pathogenic variants may harbour a higher risk. An important issue in HJT was represented by the parafibromin profile in the parathyroid tumours since in HJT both parathyroid adenomas and carcinomas might display a deficient immunoreactivity. Another frequent manifestation in HJT was ossifying fibromas of the jaw (affecting 5.4% to 50% of patients; the largest study found a prevalence of 15.4%). HJT was associated with a wide variety of kidney lesion (mostly: kidney cysts, with a prevalence of up to 75%, and renal tumours involved in 19% of patients). The risk of uterine lesions seemed increased in HJT, especially with concern to leiomyomas, adenofibromas, and adenomyosis. The underlying pathogenic mechanisms and the involvement of CDC73 pathogenic variants and parafibromin expression are yet to be explored. Currently, the heterogeneous expression of parafibromin status and, the wide spectrum of CDC73 mutations including the variety of clinical presentations in HJT, make it difficult to predict the phenotype based on the genotype. The central role of HJT-PHP is, however, the main clinical element, while the elevated risk of parathyroid carcinoma requires a special awareness.

Phenotype of Parathyroid-targeted Cdc73 Deletion in Mice Is Strain-dependent.

Hyperparathyroidism jaw-tumor syndrome is an autosomal dominant disorder caused by mutations in the CDC73/HRPT2 tumor suppressor gene, encoding parafibromin, and manifesting benign or malignant parathyroid tumors, ossifying jaw fibromas, uterine tumors, and kidney lesions. Sporadic parathyroid carcinomas also frequently exhibit inactivating CDC73 mutations and loss of parafibromin. To study the role of CDC73 in parathyroid cell proliferation in vivo, we generated mice with a parathyroid-specific deletion of Cdc73. Homozygous knockout mice on a mixed B6/129/CD1 background had decreased serum calcium and PTH and smaller parathyroid glands compared with heterozygous or wild-type littermates, whereas homozygous Cdc73-null mice on other backgrounds exhibited no abnormalities in parathyroid gland function or development. No hypercalcemia or parathyroid hypercellularity was observed in mice of any background examined at any age. Thus, although postnatally acquired complete loss of CDC73 causes parathyroid cell proliferation and hyperparathyroidism, such as seen in human hyperparathyroidism jaw-tumor syndrome, our results suggest that earlier, developmentally imposed complete loss of Cdc73 can cause a primary defect in parathyroid gland structure/function in a strain-dependent manner. This striking disparity in parathyroid phenotype related to genetic background offers a unique opportunity in an in vivo model system to precisely dissect and identify the responsible molecular mechanisms.

SAT187 A Case Of CDC73 Mutation Related Primary Hyperparathyroidism With Ectopic Parathyroid Hyperplasia

Abstract Disclosure: T. Wu: None. N. Dhir: None. M. Bollineni: None. Introduction: Primary hyperparathyroidism is the most common cause of hypercalcemia, and most cases are sporadic. However, in 5-10% cases, it may occur as a syndromic and hereditary disease, like Multiple endocrine neoplasia type 1, type 2A, type 4, or CDC73 mutation related hereditary benign or malignant hyperparathyroidism. In patients with severe or early onset primary hyperparathyroidism, screening for genetic etiology should be considered. Case Presentation: A 35-year-old woman with a medical history of hypertension, kidney stones, and post-operative hypothyroidism presented to the endocrinology clinic due to recurrent hyperparathyroidism. She initially had a parathyroidectomy in 2008 and her calcium corrected at that time. She was again diagnosed with hypercalcemia due to primary hyperparathyroidism in 2021. She underwent re-exploration and had a right thyroid lobectomy with removal of three parathyroid glands. Her PTH was still 309 pg/mL (9-77 pg/mL) and calcium was 11.2 mg/dL (8.6-10.5 mg/dL), and she was started on Cinacalcet. The patient continued to have elevated calcium, bone pain, fatigue, and constipation. A 4D CT scan was ordered, which localized activity to a 1.5 cm arterial enhancing nodule in the anterior mediastinum, with intrathymic location. She underwent right video-assisted thoracoscopic total thymectomy with en bloc and the nodule was found to be ectopic parathyroid tissue. Post-operatively, her calcium normalized to 8.6 mg/dL and PTH was undetectable. She underwent genetic testing due to her recurrent hyperparathyroidism, which showed a CDC73 mutation. She is currently on calcitriol and calcium supplements, and serum calcium has been maintained in the low-normal range. Discussion: The CDC73 gene encodes a protein called parafibromin, which acts as a tumor suppressor, prohibiting cells from proliferating. Mutations in this gene are linked to jaw-tumor syndrome, familial isolated primary hyperparathyroidism (FIHP), and parathyroid carcinoma. These three CDC73-related disorders are clinically overlapping and inherited in an autosomal dominant manner. Biallelic mutations of the CDC73 gene are associated with a high risk of parathyroid cancer since the parafibromin protein is usually absent in parathyroid carcinoma and occasionally in atypical adenomas. FIHP tends to have a more severe clinical presentation with earlier onset (younger than 45 years). Additionally, patients with CDC73 related disorders are more prone to developing ossifying fibroma(s) of the jaw, uterine tumors, and various renal lesions. In summary, this case highlights the diagnostic and therapeutic challenges in a patient with persistent primary hyperparathyroidism after a failed second surgery. Genetic testing is vital for early detection, surveillance, and familial genetic counseling in patients with CDC73 related disorders. Presentation: Saturday, June 17, 2023

SAT188 Atypical Parathyroid Adenoma: A Diagnostic Challenge Of Primary Hyperparathyroidism

Abstract Disclosure: S. Bendaram: None. L. Dulipsingh: None. Introduction: Atypical parathyroid adenomas(APA) are parathyroid neoplasms with some atypical histological features and of indeterminate malignant potential. They may occur sporadically or as a part of hereditary syndromes and contribute to 1.2-1.3% cases of Primary Hyperparathyroidism (PHPT). Here, we present an interesting case of hypercalcemia secondary to PHPT due to an underlying APA. Case Presentation: 28 year old white female with no known significant past medical history presented to ED with symptoms of nausea, vomiting and dizziness on standing. Physical examination was unremarkable except for dry mucous membranes and decreased bowel sounds. Initial labs revealed a total calcium of 19.6 mg/dl (8.4-10.2), PTH of 1161pg/ml (10-65), creatinine 1.2mg/dl (0.5-1.0), albumin 5.0 g/dl (3.5-5.0), ionized calcium 2.37 mmol/L (1.19-1.35), phosphorus 3.4 mg/dl (2.5-4.5), magnesium 1.6 mg/dl (1.7-2.8) TSH 0.51 uIU/ml (0.35-5.5), 25-hydroxy Vitamin D 24 ng/ml (30-100),1,25-dihydroxy Vitamin D 68 pg/ml (20-79) and PTHrP 19 pg/ml (11-20). Family history was negative for hypercalcemia, hyperparathyroidism, fragility fractures, pancreatic disease or any genetic syndromes. Inpatient treatment included IV fluids, 2 doses of calcitonin and Pamidronate 60 mg IV. Subsequently, over the hospital course, calcium improved to 11.9 mg/dl with improvement in her symptoms and she was discharged home. 24-hour urine calcium checked on an outpatient visit, after vitamin D replacement, revealed low urine calcium of 31 mg/24 hr. Ultrasound Thyroid demonstrated a 3.7 cm mass inferior to the right hemithyroid, suspicious for parathyroid adenoma versus abnormal lymph node. CT Parathyroid with and without contrast revealed normal thyroid and bilateral inferior parathyroid adenomas, right larger than left. She underwent en-bloc resection of right thyroid and right inferior parathyroid gland with final pathology showing atypical parathyroid adenoma, without evidence for obvious parathyroid carcinoma or metastatic disease. Genetic testing for a total of 53 genes including MEN, BRCA1, BRCA2 were negative. PTH levels normalized post-surgery. Conclusion: Atypical Parathyroid Adenomas have a clinical and biochemical profile more severe that the typical adenomas and, to some extent, similar but less severe to that of patients with parathyroid carcinoma, creating an overall diagnostic challenge. The molecular mechanisms are unclear, with germline CDC73 mutations appearing to be the most common defect. Due to uncertain malignant potential, a close and careful monitoring is recommended for these patients. Presentation: Saturday, June 17, 2023

Approach to the Patient With Parathyroid Carcinoma.

Parathyroid carcinoma (PC) is usually associated with severe symptomatic primary hyperparathyroidism (PHPT) and accounts for less than 1% of all cases of PHPT and approximately 0.005% of all cancers. PC most commonly occurs as a sporadic disease and somatic CDC73 mutations can be detected in up to 80% of cases. Approximately 30% of patients harbor a germline mutation of the CDC73 gene. Preoperative diagnosis of PC is difficult because no disease-specific markers are available, and PC should be suspected in patients with severe hypercalcemia and end-organ complications. The diagnosis is based on the evidence of invasive tumor growth at histology and/or metastases. En bloc resection of the tumor, together with the ipsilateral thyroid lobe and adjacent structures, should be performed by an experienced surgeon when PC is suspected. This surgical approach reduces the risk of recurrence and metastasis and offers the highest chance of cure. Nonetheless, PC has a recurrence rate of 40% to 60% and, if feasible, multiple surgical procedures should be performed. When surgery is no longer an option, medical treatment is aimed to reduce hypercalcemia and target organ complications. Targeted agents have been effectively used in a few cases. We describe herein a patient with severe PHPT due to PC and provide a systematic diagnostic and treatment approach. A thorough review of the medical history, a typical clinical and biochemical phenotype and, in some cases, the revision of the histological examination provide the clues for the diagnosis of PC.

Phenotypic Profiling and Molecular Mechanisms in Hyperparathyroidism-jaw Tumor Syndrome.

Hyperparathyroidism-jaw tumor (HPT-JT) syndrome is a heritable form of primary hyperparathyroidism caused by germline inactivating mutations in CDC73 encoding parafibromin and is associated with an increased risk of parathyroid cancer. There is little evidence to guide the management of patients with the disease. (1) Characterize the natural history of HPT-JT, (2) correlate genotype and histology of parathyroid tumors with parafibromin immunostaining, (3) understand molecular changes downstream to CDC73 loss. Retrospective study of patients with HPT-JT syndrome (genetically confirmed or affected first-degree relatives). Independent review of uterine tumor from 2 patients and staining for parafibromin on parathyroid tumors from 19 patients (13 adenomas, 6 carcinomas) was performed. RNA-sequencing was performed in 21 parathyroid samples (8 HPT-JT-related adenomas, 6 HPT-JT-related carcinomas, and 7 sporadic carcinomas with wild-type CDC73). We identified 68 patients from 29 kindreds with HPT-JT with median age at last follow-up of 39 [interquartile range, 29-53] years. A total of 55/68 (81%) developed primary hyperparathyroidism; 17/55 (31%) had parathyroid carcinoma. Twelve of 32 (38%) females developed uterine tumors. Of the 11 patients who had surgical resection for uterine tumors, 12/24 (50%) tumors were rare mixed epithelial mesenchymal polypoid lesions. Four of 68 patients (6%) developed solid kidney tumors; 3/4 had a CDC73 variant at p.M1 residue. Parafibromin staining of parathyroid tumors did not correlate with tumor histology or genotype. RNA-sequencing showed a significant association of HPT-JT-related parathyroid tumors with transmembrane receptor protein tyrosine kinase signaling pathway, mesodermal commitment pathway, and cell-cell adhesion. Multiple, recurrent atypical adenomyomatous uterine polyps appear to be enriched in women with HPT-JT and appear characteristic of the disease. Patients with CDC73 variants at p.M1 residue appear predisposed to kidney tumors. NCT04969926.

Genomic Profiling of the Craniofacial Ossifying Fibroma by Next-Generation Sequencing.

Ossifying fibroma (OF) of the craniofacial skeleton is a fibro-osseous lesion characterized by various patterns of bone formation in a cellular fibroblastic stroma. The molecular landscape of OF remains mostly unknown. There are a few known pathogenic abnormalities in OF, including HRPT2 mutations in conventional OF and SATB2 translocations in juvenile psammomatoid OF. On the other hand, conflicting reports exist regarding MDM2 gene amplification and chromosomal copy number alterations (CNA) in OF. Surgically removed biopsies and curettage specimens from OF patients were obtained. Clinical, radiographic, and pathologic features of tumors were reviewed. Genomic DNA was extracted from formalin-fixed, paraffin-embedded blocks of tumor tissue. Capture-based DNA next-generation sequencing targeting the coding regions 529 cancer genes and select introns was performed. We identified 17 OF cases from 8 male and 8 female patients with mean age of 22years (range 1-58years). Nine case occurred in the gnathic bones and 8 in the extragnathic craniofacial bones. These cases included 3 juvenile psammomatoid OF, 6 conventional OF and 8 juvenile trabecular OF. Large-scale CNAs were present in 6 of 17 cases. Seven cases (41%) had focal amplifications including FOSB (n = 2, 11%), FOS (n = 4, 23%), COL1A1 (n = 4, 23%) and TBX3 (n = 5, 29%). Three cases (17%) had pathogenic CDC73 mutations. No cases showed focal MDM2 amplification. Here, we provided a comprehensive molecular characterization of OF that reveals a heterogeneous genetic profile with occasional large-scale CNAs (n = 6, 35%). FOS, FOSB, and TBX3 genes that regulate AP-1 transcriptional complex are frequently altered in OF (n = 7, 41%), chiefly in juvenile trabecular OF. These genes encode transcription factors that act as downstream effectors of the MAP kinase signaling pathway. MDM2 amplification is an exceedingly rare event in OF, if present at all, so identification of this event should continue to raise concern for low-grade gnathic osteosarcoma. In summary, our findings suggest that OF represents a heterogeneous group of tumors at the genetic level but dysregulation of the AP-1 pathway may play a role in pathogenesis of juvenile trabecular OF.

Familial parathyroid tumours-comparison of clinical profiles between syndromes.

Primary hyperparathyroidism (PHPT) caused by parathyroid tumours is mostly sporadic, with a genetic cause identified in 5-10% of cases. Familial parathyroid tumours can be included in complex syndromes, such as multiple endocrine neoplasia (MEN) type 1, 2A and 4 or hyperparathyroidism-jaw tumour syndrome (HPT-JT). Characterisation of the familial parathyroid tumours followed-up at our centre and comparison of the different clinicopathological manifestations between the syndromes. Retrospective analysis of 48 patients with familial parathyroid tumours harbouring RET (n = 11), CDC73 (n = 20) and MEN1 (n = 17) germline mutations was performed. Cases of PHPT in MEN2A syndrome presented with lower serum PTH (sPTH) and serum calcium (sCa) levels at diagnosis (sPTH = 108.0 (IQR 53.3) pg/mL, sCa = 10.6 ± 1.1mg/dL) than MEN1 (sPTH = 196.9 (IQR 210.5) pg/mL, sCa = 11.7 ± 1.2mg/dL) (p = 0.01, p = 0.03, respectively) or HPT-JT cases (sPTH = 383.5 (IQR 775.8) pg/mL, sCa = 12.9 ± 1.8mg/dL) (p = 0.01; p < 0.001, respectively). There was a statistical difference in sCa levels between MEN1 and HPT-JT (p = 0.02), but not between sPTH (p = 0.07). The predominant first manifestation of the syndrome in MEN1 was gastroenteropancreatic neuroendocrine tumour (GEP-NET) in 47.1% of the cases, in MEN2A was medullary thyroid cancer (90.9%) and in HPT-JT was PHPT in 85% patients. In MEN1 syndrome, the number of affected parathyroid glands was significantly higher than in MEN2A (p < 0.001) and HPT-JT (p = 0.01). The first manifestation of the syndrome in MEN1 cases was GEP-NET and not PHPT. Although presenting at similar ages, patients with MEN2A exhibit less severe biochemical and clinical PHPT at diagnosis than the other familial syndromes.

Clinical and genetic analysis of atypical parathyroid adenoma compared with parathyroid carcinoma and benign lesions in a Chinese cohort.

The malignant potential and molecular signature of atypical parathyroid adenoma (APA) remain elusive. Data from Asia are still lacking. This was a retrospective study on a large APA cohort in a single center from mainland China. A total of 320 patients with primary hyperparathyroidism (PHPT), containing 79 APA, 79 Parathyroid cancer (PC) and 162 benign lesions cases, were enrolled after surgery for collection of clinical data and genetic analysis. APA patients showed earlier mean onset age than benign group (46.9 ± 17.1 vs. 52.0 ± 14.3 yrs). Less bone involvement and gastrointestinal symptoms were presented in APA compared to PC (35.4% vs. 62.0%, and 17.7% vs. 41.8%), while more urolithiasis was seen in APA than in benign lesions (57.0% vs. 29.6%). The APA group had moderate hypercalcemia (mean 3.02 ± 0.44mmol/L) with elevated serum PTH (median 593.0pg/ml) and proportion of hypercalcemic crisis as 22.8%, all higher than those of benign lesions but lower than those of PC group. The recurrence/no remission rate of the APA group was significantly lower than that of the PC and similar to the benign group (5.1% vs. 31.6% vs. 3.1%). Germline CDC73 mutation was the most common molecular abnormality in both PC and APA subjects. APA patients with nonsynonymous germline variants showed earlier onset age (28.5 ± 16.9 vs. 48.1 ± 17.7 yrs) and more cases developing no remission/recurrence (25.0% vs. 0.0%). Patients with APA presented clinical and biochemical characteristics much less severe than PC and resembling the benign neoplasms, with a relatively good prognosis. Germline gene variations were associated with earlier onset and probably more recurrence of PHPT in APA.

Genomic Profiling Reveals the Variant Landscape of Sporadic Parathyroid Adenomas in Chinese Population.

To define somatic variants of parathyroid adenoma (PA) and to provide novel insights into the underlying molecular mechanism of sporadic PA. Basic clinical characteristics and biochemical indices of 73 patients with PA were collected. Whole-exome sequencing was performed on matched tumor-constitutional DNA pairs to detect somatic alterations. Functional annotation was carried out by ingenuity pathway analysis afterward. The protein expression of the variant gene was confirmed by immunohistochemistry, and the relationship between genotype and phenotype was analyzed. Somatic variants were identified in 1549 genes, with an average of 69 variants per tumor (range, 13-2109; total, 9083). Several novel recurrent somatic variants were detected, such as KMT2D (15/73), MUC4 (14/73), POTEH (13/73), CD22 (12/73), HSPA2 (12/73), HCFC1 (11/73), MAGEA1 (11/73), and SLC4A3 (11/73), besides the previously reported PA-related genes, including MEN1 (11/73), CASR (6/73), MTOR (4/73), ASXL3 (3/73), FAT1 (3/73), ZFX (5/73), EZH1 (2/73), POT1 (2/73), and EZH2 (1/73). Among them, KMT2D might be the candidate driver gene of PA. Crucially, 5 patients carried somatic mutations in CDC73, showed an aggressive phenotype similar to that of parathyroid carcinoma (PC), and had a decreased expression of parafibromin. Pathway analysis of recurrent potential PA-associated driver variant genes revealed functional enrichments in the signaling pathway of Notch. Our study expanded the pathogenic variant spectrum of PA and indicated that KMT2D might be a novel candidate driver gene and be considered as a diagnostic biomarker for PA. Meanwhile, CDC73 mutations might be an early developmental event from PA to PC. The results provided insights into elucidating the pathogenesis of parathyroid tumorigenesis and a certain basis for clinical diagnosis and treatment.

PSAT211 Low Grade Parathyroid Carcinoma: A Challenging Diagnosis in the Evaluation of Primary Hyperparathyroidism

Abstract Background Parathyroid carcinoma often presents with severe symptomatic hypercalcemia, bone and kidney involvement, and PTH &amp;gt; 4x the upper limit of normal. Diagnosis is challenging and requires classic pathologic findings. Case Presentation A 34-year-old woman presented with hypercalcemia. She was found to have primary hyperparathyroidism with elevated total calcium (11.8 mg/dL), elevated PTH (352.8 pg/mL), and elevated 24-hour urine calcium (758 mg/24hr). A 99mTc sestamibi scan showed focal uptake in the right inferior thyroid pole. Intraoperatively, there was a lobulated, fibrotic right parathyroid mass sized 3.5×2.5×2.0 cm. Pathology showed low-grade parathyroid carcinoma with lymphovascular invasion, extension into soft tissue, and focal positivity in resection margin. Post-operative PTH was 19.5 pg/mL. One month later, PTH was elevated to 82.0 pg/mL with calcium of 9.1 mg/dL. PET scan did not show metastases. The patient then underwent a right thyroid lobectomy with central compartment lymph node dissection. Pathology showed residual parathyroid carcinoma within the perithyroidal scar tissue but was negative for lymph node involvement. Postoperatively, her PTH was 52.5 pg/mL. Genetic studies showed no mutations in CDC73, MEN1, RET, RB1, and TP53 genes. She underwent external beam radiation treatment. Following radiation, her total calcium and PTH level remained in the normal range with no recurrence on thyroid ultrasound. Clinical Lessons On ultrasound, parathyroid carcinomas are large, have increased heterogeneity and lobulations, as well as suspicious lymph nodes. Intraoperative suspicion is based on large size, capsular or local tissue invasion, and lymph node metastases. Histologic assessment can be challenging as findings of parenchymal mitoses, trabeculated parenchyma, and thick fibrous bands are also seen with parathyroid adenomas. Local tissue invasion (angiolymphatic, perineural or adjacent structures) or metastases such as lymph nodes seen on pathology are diagnostic of parathyroid carcinoma. PET can be used post-operatively to identify recurrence or metastases. Genetic studies especially for mutations in CDC73 can be helpful in diagnosis as it is the most common cause of syndromic and sporadic parathyroid carcinoma.Resection of the tumor and adjacent tissues is the mainstay of treatment. A regional lymph node dissection should be done if there are suspicious lymph nodes. Neither thyroidectomy, chemotherapy nor radiation has been shown to improve overall survival. Radiation has shown to have some benefit for local recurrence and disease-free survival. Lifelong monitoring of calcium and PTH levels is required, and if elevated, should prompt imaging with thyroid ultrasound and PET scan. Prognosis is generally poor but does improve if there is complete surgical resection on initial diagnosis. Almost all patients experience recurrence within 2-23 years after resection Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.

PSAT198 Atypical Parathyroid Adenoma is an Unusual Cause of Primary Hyperparathyroidism

Abstract Background Atypical parathyroid adenomas (APA) are considered tumors of uncertain malignant potential and have a biochemical and clinical phenotype that is generally more aggressive than typical parathyroid adenomas (PA). Low incidence as an etiology of primary hyperparathyroidism (PHPT) presents a challenge in understanding the pathological features and natural history of APA. We present a case of PHPT due to an APA and review the published literature for these tumors. Case A 37 year-old male was referred for evaluation of hypercalcemia, with serum calcium level 13.6 mg/dL (8.6-10.3). Repeat serum calcium measurement was 12.7 mg/dL, and two measurements of intact PTH were 870 pg/mL and 919 pg/mL (12-88), respectively. The patient's laboratories raised concern for parathyroid carcinoma (PC), but there was no palpable neck mass and no enlarged parathyroid glands were visualized on ultrasonography. Parathyroid scintigraphy was notable for faint but persistent Tc-99 m sestamibi uptake in the left inferior neck. Additional preoperative evaluation revealed significantly reduced bone mineral density in the distal third of the radius (0.638 g/cm2, Z-score -3.2), silent nephrolithiasis of the right kidney, and vitamin D deficiency (25-OH vitamin D 13.4 ng/dL, 30-100). An unequivocally enlarged (175 mg, 2.5 cm in largest diameter) left inferior parathyroid gland was removed, with the remaining glands unremarkable by inspection. Extensive nuclear atypia and cellular pleomorphism indicated an APA, and invasive features of PC were absent. One month after surgery, serum calcium improved to 10.2 mg/dL and intact PTH was 40 pg/mL. Conclusions APA account for 1-2% of PHPT cases. This patient's case has several features that distinguish it from a PA including degrees of preoperative hypercalcemia and intact PTH elevation, low vitamin D level, significantly reduced bone density in the distal third of the radius, nephrolithiasis, relatively young age, and male gender. Fibrous bands, pseudocapsular invasion, and trabecular growth pattern are the most common histologic features of APA, but nuclear atypia and cellular pleomorphism are well established diagnostic criteria. APA may be biochemically similar to PC but are distinguished from PC by the absence of gross invasion into adjacent anatomic structures, distant metastases, and vascular or perineural invasion. Additionally, CDC73 mutations are present in nearly all cases of PC but not in APA. Over 90% of patients with APA are successfully treated by parathyroidectomy. Careful follow up of APA patients is recommended, though there are no specific guidelines regarding a minimum satisfactory duration of postsurgical monitoring. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.