Continuing Education Activity

Parathyroid carcinoma is a rare but aggressive endocrine malignancy accounting for less than 1% of primary hyperparathyroidism cases, which typically presents in midadulthood with severe hypercalcemia, markedly elevated parathyroid hormone levels, and a palpable neck mass. While most cases are sporadic, genetic associations include multiple endocrine neoplasia (MEN) types I and IIa and hyperparathyroidism-jaw tumor syndrome. This course reviews diagnostic processes that rely on histopathologic evidence of capsular or vascular invasion, with parafibromin loss aiding in the distinction from benign lesions. Imaging modalities that play critical roles in localization as well as staging and surgical resection with en bloc removal, which remains the cornerstone of treatment, are also discussed. 

This course explores the clinical features, diagnostic strategies, and evolving management approaches of parathyroid carcinoma, including the need for long-term surveillance to optimize outcomes due to the high frequency of recurrence. Participants will also gain an understanding of high-risk presentations, the integration of multimodal imaging, and the application of evidence-based surgical and medical management principles. This activity for healthcare professionals is designed to enhance the learner's competence in identifying parathyroid carcinomas, performing the recommended evaluation, and implementing an appropriate interprofessional approach when managing this condition to improve diagnostic accuracy, implement timely interventions, manage complications of hypercalcemia, and enhance patient-centered care and long-term outcomes for this complex and rare malignancy.

Objectives:

• Differentiate diagnostic features that differentiate parathyroid carcinoma from benign primary hyperparathyroidism.
• Evaluate appropriate surgical management strategies for parathyroid carcinoma, including en bloc resection.
• Develop strategies for individualized treatment planning for parathyroid carcinoma, based on tumor characteristics, the extent of disease, and patient-specific factors.
• Coordinate interprofessional collaboration to improve timely diagnosis, individualized treatment planning, and comprehensive postoperative management for patients with parathyroid carcinoma.

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Introduction

Parathyroid carcinoma represents a rare malignancy of the parathyroid glands, most often arising sporadically but sometimes associated with genetic syndromes, eg, multiple endocrine neoplasia (MEN) syndrome types I and IIa and hyperparathyroidism-jaw tumor (HPT-JT) syndrome. This carcinoma accounts for fewer than 1% of primary hyperparathyroidism cases and occurs equally in men and women, most commonly during midadulthood. Loss of tumor suppressor function, frequently through HRPT2/CDC73 mutations, drives disease progression by promoting excessive hormone secretion and aggressive local invasion.

Histopathologic confirmation requires identification of capsular or vascular invasion, while parafibromin loss assists in distinguishing carcinoma from benign lesions. Clinically, suspicion increases with the presence of a firm neck mass accompanied by severe hypercalcemia, making comprehensive history-taking and physical examination essential for early recognition. Biochemical testing and imaging modalities, including ultrasound, sestamibi scanning, and 4-dimensional computed tomography (4D-CT), guide lesion localization, and advanced positron emission tomography/computed tomography (PET/CT) techniques contribute to the detection of metastatic disease.[1]

En bloc surgical resection remains the primary treatment and offers the best chance for long-term survival, though recurrence frequently complicates outcomes and often necessitates systemic therapy or targeted medical management. Differential considerations include benign parathyroid adenomas, thyroid nodules, and metastatic tumors, yet no standardized staging system exists. Prognosis depends largely on early complete resection, while recurrence and hypercalcemia drive long-term morbidity and mortality. Complications stem both from the endocrine effects of the tumor and from risks associated with surgical and medical interventions. Effective patient education, combined with interprofessional coordination, ensures timely diagnosis, appropriate treatment, and structured long-term surveillance in this challenging disease.

Etiology

Most parathyroid carcinomas develop sporadically and without a clear cause, although well-documented associations exist with MEN syndrome types I and IIa, as well as with HPT-JT syndrome.[2][3] Parathyroid carcinoma represents fewer than 1% of all primary hyperparathyroidism cases, yet reports describe an incidence as high as 5%. The origin of this malignancy remains uncertain. Some researchers hypothesize that parathyroid carcinoma may develop in the setting of primary parathyroid hyperplasia, although malignant transformation of benign lesions remains a theoretical possibility rather than a proven pathway.[1]

Mutations in HRPT2 (CDC73), a tumor suppressor gene, play a central role in the molecular pathogenesis of parathyroid carcinoma. Located on chromosome 1, HRPT2 encodes parafibromin, a protein that regulates cell proliferation through inhibitory mechanisms. Loss-of-function mutations involving this gene appear in both sporadic cases and HPT-JT–related parathyroid carcinomas. Patients with HPT-JT face additional risks, including ossifying fibromas of the jaw, renal cysts, and renal neoplasms, which contribute to their increased susceptibility. Approximately 15% of individuals with HPT-JT develop parathyroid carcinoma, underscoring the importance of early recognition and surveillance in this high-risk population.[4][5][6]

Epidemiology

Parathyroid carcinoma represents an exceptionally rare malignancy, accounting for fewer than 1% of primary hyperparathyroidism cases and only 0.005% of all cancers.[7] The estimated annual incidence ranges from 3 to 7 cases per 10 million individuals, with reports indicating a gradual increase in recent decades, most likely due to improved diagnostic methods and more accurate reporting.

The disease typically presents in middle to late adulthood, with the average age at diagnosis falling between the early fifth and sixth decades of life.[8] Unlike benign primary hyperparathyroidism, which occurs more frequently in women, parathyroid carcinoma affects men and women at nearly equal rates. Most reported cases involve Caucasian populations, highlighting demographic trends that may reflect both genetic and diagnostic factors.[9]

Pathophysiology

Parathyroid carcinoma arises from a loss of parafibromin, leading to dysregulation of the cell cycle and uncontrolled cellular proliferation. This causes excessive parathyroid hormone (PTH) secretion, and as a result, many patients experience severe, refractory hypercalcemia with subsequent systemic complications like nephrolithiasis, bone pain, osteoporosis, fractures, gastrointestinal disturbances, cardiac instability, and neurocognitive symptoms.

A palpable neck mass, typically hard, firm, and adherent to surrounding tissues, is reported in a subset of patients and may serve as a distinguishing clinical clue compared to benign parathyroid disease. Tumors are often 2 to 4 cm in size at diagnosis and frequently demonstrate direct extension into adjacent structures, most commonly the ipsilateral thyroid lobe.[10] In fact, adherence to surrounding tissues is reported in up to 78% of cases, and capsular invasion remains a defining histopathologic hallmark.

Local spread into the thyroid, strap muscles, trachea, or esophagus is well-documented, while regional lymph node involvement is observed in approximately one-quarter of patients. Distant metastases are less common at presentation but occur in a significant minority, most often to the lungs, liver, or bone, and disease recurrence with metastatic spread represents a major driver of long-term morbidity and mortality. The aggressive local behavior and metastatic potential clearly differentiate parathyroid carcinoma from benign parathyroid neoplasms.[11][12][13][14]

Histopathology

Parathyroid carcinoma is grossly characterized as a firm, gray-white, lobulated mass that is usually larger than benign parathyroid tumors, lacks a distinct capsule, and is adherent to adjacent structures with local invasion. The entire gland is generally traversed by broad fibrous bands that originate from the capsule and extend to the tumor, which results in a lobulated appearance.[15]

Histologically, the diagnosis of malignancy requires evidence of invasive growth, which may include vascular or lymphatic invasion, perineural infiltration, direct extension into adjacent structures, or metastatic spread. The cells may be clear, oxyphilic, uniformly bland, or show metaplasia and are arranged in nests or trabeculae. The cells with minimal atypia may be challenging to differentiate from those of a parathyroid adenoma. Although mitotic figures are a primary factor in diagnosing parathyroid carcinoma, they are also present in adenomas and hyperplasia. Thus, their absence does not rule out the possibility of carcinoma.[16]

Because traditional histologic parameters can be equivocal, immunohistochemistry serves as a valuable adjunct to diagnosis. Loss of parafibromin expression, reflecting inactivation of the CDC73 (HRPT2) tumor suppressor gene, strongly supports the diagnosis of carcinoma over benign lesions. However, the absence of this marker does not rule out malignancy.[17]

History and Physical

Clinical Features

A thorough head and neck evaluation remains critical in assessing suspected parathyroid carcinoma. Approximately 50% of patients present with a palpable central neck mass in addition to systemic manifestations of hypercalcemia and hyperparathyroidism, including kidney stones, arrhythmias, osteoporosis, or fractures. The coexistence of a palpable neck mass with biochemical evidence of hyperparathyroidism or hypercalcemia strongly suggests malignancy. A detailed endocrine history and family history should be obtained to screen for occult MEN syndromes, while documentation of prior ionizing radiation to the head and neck is equally important, as rare cases of parathyroid carcinoma have been reported following such exposure.

The physical examination should include careful inspection and palpation of the oral cavity, jaw, and neck. Palpation of the lateral and central neck should assess for masses and lymphadenopathy, with focused attention on the thyroid gland at rest and during deglutition. The clinician should also evaluate voice quality and vocal strength, maintaining a low threshold for flexible laryngoscopy or stroboscopy to identify subtle vocal fold weakness, which may indicate involvement of the recurrent laryngeal nerve.[18]

Evaluation

Evaluation of parathyroid carcinoma requires a combination of biochemical, clinical, and imaging assessments to accurately identify malignancy, guide surgical planning, and detect metastatic or recurrent disease. Early recognition relies on integrating laboratory findings with physical examination and advanced imaging, as clinical presentation often overlaps with benign hyperparathyroid disorders. A structured, multimodal approach enhances diagnostic accuracy and informs interprofessional management strategies.

Biochemical and Clinical Assessment

Patients frequently present with symptomatic, severe hypercalcemia (serum calcium often >14 mg/dL) and markedly elevated PTH levels, which are typically higher than levels seen in benign primary hyperparathyroidism (PHPT). A PTH 3 times the upper limit of normal is suspicious for malignancy, while a PTH of 10 times the upper limit of normal has a positive predictive value of 84% for parathyroid carcinoma. Clinically, a palpable neck mass is present in the majority of cases, a finding that is unusual in benign parathyroid disease. Patients frequently present with end-organ complications of hypercalcemia, eg, nephrolithiasis, bone disease, fractures, and neurocognitive disturbances.[19][20]

Imaging Studies

Ultrasound

Ultrasound serves as the most frequently used imaging modality for evaluation. Lesions greater than 3 cm, irregular or infiltrative margins, heterogeneous echotexture, decreased echogenicity, and a depth-to-width ratio of 1 or greater are findings that raise concern for carcinoma rather than a benign parathyroid adenoma. The presence of suspected tissue invasion on ultrasound should further heighten suspicion for malignancy.[21]

Technetium Tc 99m sestamibi scintigraphy

Technetium Tc 99m sestamibi scintigraphy remains the standard radionuclide imaging technique for parathyroid disease and is often combined with ultrasound to improve diagnostic accuracy. Reported sensitivities for sestamibi and ultrasound individually are approximately 71% and 77%, respectively, with specificity approaching 100% when both are used together.[22] While sestamibi is highly useful in detecting hyperfunctioning parathyroid tissue, its ability to distinguish benign parathyroid disease from malignant lesions is limited.

Computed tomography

CT provides important information regarding local tumor invasion and metastatic disease. Findings suggestive of malignancy include irregular morphology, peritumoral infiltration, calcifications, and a high short-to-long axis ratio. Imaging with 4D-CT has emerged as a particularly valuable modality, particularly in patients with negative sestamibi scans or distorted neck anatomy. Multiphasic imaging provides excellent localization of hyperfunctioning parathyroid tissue, with reported sensitivities exceeding 90% and specificities approaching 100% in some series.[23] When combined with ultrasonography and sestamibi, the diagnostic yield improves further. However, despite these advantages in lesion localization, 4D-CT has a limited ability to reliably distinguish parathyroid carcinoma from benign parathyroid adenoma or hyperplasia, underscoring the need for histopathologic confirmation.

Positron emission tomography/computed tomography imaging

An 18F-fluorocholine (18F-FCH) PET/CT offers superior resolution and shorter acquisition times compared to sestamibi and has demonstrated improved sensitivity for detecting small or ectopic parathyroid lesions. Dual-tracer approaches combining 18F-FCH and 18F-fluorodeoxyglucose (18F-FDG) may provide additional value in staging metastatic disease, with reports of identifying metastases not seen on FDG alone. Although further validation is needed, PET/CT is proving to be an important adjunct in the comprehensive evaluation of parathyroid carcinoma.[24]

Magnetic resonance imaging

Magnetic resonance imaging (MRI) can assist in characterizing local disease and may be particularly useful in evaluating recurrence. The role of this modality in primary preoperative differentiation between adenoma and carcinoma remains limited; however, MRI provides an alternative when other imaging techniques are inconclusive or contraindicated.

Dual-energy x-ray absorptiometry

Dual-energy x-ray absorptiometry (DEXA) scans may be used to evaluate for osteoporosis, but they are not highly specific for parathyroid carcinoma. While DEXA scanning does not contribute to the direct diagnosis of parathyroid carcinoma, this modality is valuable for assessing bone mineral density, quantifying skeletal complications at presentation, and monitoring recovery following successful surgical management. 

Treatment / Management

Management of parathyroid carcinoma presents significant challenges due to its rarity, diagnostic complexity, and high risk of recurrence. Surgical resection remains the definitive treatment, with complete en bloc removal during the initial operation offering the highest likelihood of long-term survival. Despite optimal surgical intervention, recurrence develops in 60% to 80% of patients, underscoring the aggressive nature of this malignancy.

For unresectable or metastatic disease, systemic and supportive medical therapies play a central role in controlling hypercalcemia, which serves as the primary contributor to morbidity and mortality. Emerging roles for radiation therapy and systemic oncology treatments are primarily guided by case reports and small clinical series, reflecting the limited evidence base. Effective management requires an interprofessional approach that integrates the expertise of surgical oncology, radiation oncology, and medical oncology.[7] Coordination across these specialties ensures timely intervention, optimized patient outcomes, and comprehensive care for this complex endocrine malignancy.

Differential Diagnosis

Parathyroid carcinoma presents similarly to primary hyperparathyroidism with elevated levels of parathyroid hormone and serum calcium. The differential diagnosis consists of several benign and malignant conditions that must be carefully distinguished, including:

• Parathyroid adenoma: Most common cause of primary hyperparathyroidism, usually smaller and without a palpable mass
• Parathyroid hyperplasia: Multiple gland involvement, often associated with familial syndromes
• Paraneoplastic syndrome: Elevated serum calcium with elevated parathyroid hormone-related peptide rather than PTH
• Thyroid nodule: May be difficult to distinguish from parathyroid neoplasms, but both present with a palpable neck mass
• Primary thyroid malignancy: Requires imaging and biopsy for differentiation
• Brown tumor: Osteolytic lesions that can occur with severe hyperparathyroidism

Surgical Oncology

Surgical intervention, typically parathyroidectomy with or without ipsilateral thyroidectomy, represents the preferred treatment for parathyroid carcinoma. When preoperative evaluation indicates a high suspicion of malignancy, parathyroidectomy should be performed with en bloc resection of the ipsilateral thyroid and any adjacent tissues showing evidence of invasion. If final histopathology demonstrates positive margins, repeated resection aimed at achieving margin clearance is recommended. Such procedures can be technically complex and may require tracheal or esophageal resection, occasionally necessitating the sacrifice of the recurrent laryngeal nerve. Careful preoperative planning and thorough patient counseling regarding potential reconstructive procedures remain essential.

Local or regional recurrence should be addressed surgically whenever feasible, as excision often provides significant palliation of hypercalcemia even if long-term cure remains uncertain. Resection of isolated metastatic lesions, including pulmonary or hepatic deposits, has been performed in select cases for symptom management, although comprehensive survival data remain limited. Overall, aggressive surgical management remains the cornerstone strategy for controlling disease progression, alleviating hypercalcemia, and improving patient quality of life.[25][26]

Radiation Oncology

External beam radiotherapy (EBRT) has not been shown to improve overall survival in parathyroid carcinoma, as demonstrated in extensive database analyses, even among patients with regionally advanced disease. While small series suggest EBRT may reduce local recurrence, its routine use is not recommended and should be reserved for select high-risk or unresectable cases.[27]

Medical Oncology

When parathyroid carcinoma becomes unresectable due to extensive metastatic disease, medical management focuses on controlling hypercalcemia, the primary driver of morbidity. Acute hypercalcemic crises are initially addressed with intravenous hydration using normal saline, often combined with loop diuretics to enhance renal calcium excretion. Adjunctive therapies include calcitonin, which provides short-term calcium reduction despite tachyphylaxis, bisphosphonates (eg, zoledronic acid or pamidronate), and denosumab, particularly useful in patients with renal impairment or resistance to bisphosphonates. For refractory hypercalcemia, the calcimimetic cinacalcet effectively lowers serum calcium, and dialysis may be required in severe cases. Cytotoxic chemotherapy has historically demonstrated limited efficacy; however, isolated responses to alkylating agents, such as temozolomide, have been reported in specific molecular contexts, including O(6)-methylguanine-DNA-methyltransferase (MGMT) promoter methylation.[28][29]

Emerging targeted therapies have shown promise for nonoperative management. Case reports and small series describe biochemical responses and prolonged disease stabilization using VEGF-directed tyrosine kinase inhibitors, including lenvatinib and surufatinib. Individualized approaches guided by genomic profiling have employed immune checkpoint inhibition with pembrolizumab for tumors with high mutational burden, multireceptor tyrosine kinase inhibition for FGFR1 and RET overexpression, and PARP inhibition with olaparib in patients with defective homologous recombination repair.[30][31] These observations highlight the potential of precision medicine in managing advanced parathyroid carcinoma, although prospective clinical trial data remain limited.

Staging

No standardized tumor, node, metastases (TNM) staging system exists for parathyroid carcinoma. The American Joint Committee on Cancer noted in the 2017 edition of the TNM Cancer Staging Manual that establishing formal staging for this malignancy would be premature due to its rarity and the limited evidence base guiding prognostic classification.

Prognosis

Parathyroid carcinoma has a relatively favorable short-term prognosis but a poor long-term outlook due to frequent recurrence and progressive hypercalcemia. According to SEER-based data analysis, 5-year overall survival rates are 84% following surgery, with a median overall survival of nearly 14 years. Recurrence rates occur in up to 60% of patients within 2 to 5 years after initial resection. Complete surgical excision at the initial operation remains the strongest predictor of survival, while advanced age, nodal/distant metastases, and aggressive histologic features are associated with worse outcomes.[7][32]

Complications

The complications of parathyroid carcinoma are primarily driven by excessive PTH secretion and sustained hypercalcemia, rather than tumor bulk. Persistent hypercalcemia can be refractory to medical management or unresectable disease. Renal complications include nephrolithiasis and eventual chronic kidney disease. Skeletal involvement includes bone pain, significant reductions in bone mineral density, and osteoporotic fractures. Cardiovascular effects of prolonged hypercalcemia may include hypertension, arrhythmias, or cardiac calcifications. Patients may also develop neurocognitive symptoms, eg, fatigue, depression, and confusion.

Risks inherent to surgical management include vocal cord paralysis, hypoparathyroidism, and bleeding. Recurrent laryngeal nerve injury is a known complication of aggressive or repeated neck surgery, especially when the tumor is invasive. In rare cases, tracheal or esophageal invasion may necessitate complex resections with reconstruction. Medical therapy, particularly with bisphosphonates or denosumab, carries potential risks (eg, osteonecrosis of the jaw and renal toxicity).

Deterrence and Patient Education

Deterrence and patient education play a crucial role in managing parathyroid carcinoma, as early recognition and intervention have a significant impact on long-term outcomes. Because this rare malignancy often mimics benign parathyroid disease, clinicians must educate patients with primary hyperparathyroidism about warning signs, eg,  a firm neck mass, persistent or severe hypercalcemia, kidney stones, bone pain, or neurocognitive changes. Clear communication about the importance of routine biochemical monitoring, imaging, and prompt evaluation of new or worsening symptoms helps reduce diagnostic delays and improves the likelihood of detecting disease at a surgically curable stage. Educating patients with known genetic risk factors, eg, those with MEN syndromes or hyperparathyroidism-jaw tumor syndrome, further supports deterrence through targeted surveillance and early intervention.

Patient education must also emphasize the lifelong nature of follow-up and the potential for recurrence, even after complete tumor removal. Individuals benefit from understanding the need for ongoing calcium and parathyroid hormone monitoring, bone health assessments, and imaging when indicated. Education should include strategies for managing hypercalcemia symptoms, adherence to prescribed therapies such as bisphosphonates, cinacalcet, or denosumab, and awareness of potential surgical or medication-related complications. By promoting shared decision-making, providing psychosocial support, and fostering open communication between patients and the interprofessional team, education efforts empower individuals to participate actively in their care. This collaborative approach enhances safety, supports long-term quality of life, and helps mitigate the risks associated with this challenging malignancy.

Enhancing Healthcare Team Outcomes

Parathyroid carcinoma is a rare endocrine malignancy that represents fewer than 1% of primary hyperparathyroidism cases. It often presents with severe hypercalcemia, markedly elevated parathyroid hormone levels, and a palpable neck mass. Most cases are sporadic, but associations with multiple endocrine neoplasia and hyperparathyroidism-jaw tumor syndrome highlight the genetic underpinnings of the disease. Diagnosis requires careful integration of clinical features, advanced imaging, and histopathologic confirmation, while en bloc surgical resection offers the best chance for long-term survival. Given the high recurrence rates and morbidity related to hypercalcemia, ongoing surveillance and coordinated care remain essential.

Effective management relies on an interprofessional approach that maximizes team performance and patient-centered care. Physicians, surgeons, endocrinologists, radiologists, pathologists, advanced practitioners, and nurses collaborate to ensure early recognition, accurate diagnosis, and timely surgical intervention. Pharmacists contribute by guiding safe and effective medical therapy for refractory or recurrent disease. Interprofessional communication through case conferences, tumor boards, and shared records fosters coordinated decision-making, enhances patient safety, and reduces complications. By integrating specialized expertise, healthcare teams improve outcomes, support patient education, and sustain long-term quality of life for individuals living with parathyroid carcinoma.

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Disclosure: Alexandra Helbing declares no relevant financial relationships with ineligible companies.

Disclosure: Gopal Menon declares no relevant financial relationships with ineligible companies.