A germline mutation of HRPT2/CDC73 (70 G>T) in an adolescent female with parathyroid carcinoma: first case report and a review of the literature

Introduction

Primary hyperparathyroidism is very rare in children and adolescents, with an estimated incidence of 2–5 in 100,000 [1]. Parathyroid carcinoma is a rare cause of primary hyperparathyroidism, with a reported incidence of 0.4–5% of hyperparathyroid-related hypercalcemia [2], [3], [4], [5], [6]. Additionally, parathyroid carcinoma only accounts for 0.005% of all malignancies [7]. As a result, a relative paucity of literature exists on parathyroid carcinoma. Furthermore, parathyroid carcinoma amongst children and adolescents is exceedingly rare, with only nine previously reported cases in the English literature occurring in children under the age of 16 [2], [8], [9], [10], [11], [12], [13], [14], [15]. None of these cases has had documented HRPT2/CDC73 gene mutation analysis. We report the tenth case, which is also the first pediatric case to have a reported HRPT2/CDC73 mutation.

Materials and methods

Results

Case description

A previously healthy 14-year-old Hispanic girl suffered from chronic leg pain since 6 years of age and her pediatrician repeatedly reassured the parents that this was likely due to ‘growing pains’. At 7 years old she was diagnosed with severe thoracolumbar scoliosis for which she was seen by an orthopedist and was prescribed a brace, to which she had poor treatment adherence. She developed progressive bowing of her legs together with worsening leg pain as well as bilateral groin pain that gradually increased in severity. She started to limp, and her symptoms worsened to the point where she could only walk very short distances and otherwise had to be carried. At that time, she presented to an orthopedist and was found to have a right-sided slipped capital femoral epiphysis (SCFE). The patient underwent in situ fixation of the right femur. The patient was found to have hypercalcemia of 3.05 mmol/L (12.2 mg/dL) at the time of orthopedic intervention, which warranted further work up and referral to endocrinology. Several months later, upon our initial evaluation, the patient reported diffuse bone pain most notably in her knees, increased thirst, insomnia, fatigue and difficulty concentrating at school. She also reported mild globus sensation when swallowing solid foods but denied abdominal pain. She had no history of renal disease or thyroid dysfunction. There was no family history of thyroid, parathyroid, or renal disease. On physical examination, the patient had a left anterior 3×3 cm neck mass. Pertinent preoperative laboratory data included serum total calcium of 3.4 mmol/L (13.4 mg/dL, reference range, 8.4–10.2 mg/dL), phosphorus 1.1 mmol/L (3.5 mg/dL, reference range 2.5–4.5 mg/dL), intact parathyroid hormone (iPTH) of 1013 ng/L (1013 pg/mL, reference range, 9–69 pg/mL), 25-OH vitamin D of <12.5 nmol/L (<5 ng/mL, sufficient >30 ng/mL), 1,25-OH vitamin D of 369.2 pmol/L (142 pg/mL, reference range 19–83 pg/mL), serum albumin of 43 g/L (4.3 g/dL, reference range, 3.2–4.5 g/dL), spot urine calcium of 5.6 mmol/L (22.4 mg/dL), spot urine creatinine of 6895 mmol/L (78 mg/dL), urine calcium:creatinine ratio of 0.29. All other laboratory values were within normal limits.

A ^99mTechnetium (Tc)-Sestamibi scan demonstrated a large extrathyroidal ^99mTc uptake at the left inferior thyroid pole that persisted at the 3-h mark, suspicious for parathyroid adenoma. A high-resolution ultrasound of the neck found a well-defined extrathyroidal mass at the inferior aspect of the left thyroid lobe that correlated with the ^99mTc-Sestamibi scan. The mass measured 3.3×2.3×2.9 cm with central heterogeneous echogenicity, soft tissue echogenicity, and some cystic portions, giving it an unusual appearance for a parathyroid adenoma.

The patient underwent left neck exploration and parathyroidectomy with recurrent laryngeal nerve monitoring. At the time of surgery, a firm, 3.5×3×1.3 cm left inferior parathyroid mass was encountered, and found to be adherent to surrounding tissues, including the anterior tracheal wall fascia, the left inferior thyroid, and the left thymic tongue; thus, a wide local excision was performed. There was no cervical adenopathy identified in the tracheoesophageal groove, but the left recurrent laryngeal nerve was significantly displaced laterally by the tumor. En-bloc resection of the tumor along with a left inferior thyroid lobectomy was performed. The performed neck dissection included an ipsilateral selective neck dissection of levels III and IV from the left common carotid artery laterally to the anterior tracheal wall fascia medially and a complete level VI lymph node dissection down to the brachiocephalic artery including the thymic tongue. The neck exploration was limited to the ipsilateral and central neck compartments as the tumor did not cross midline, intraoperative frozen sections on all surgical margins were negative for tumor, and there was no clinical lymphadenopathy observed. The surgical specimen was dark red-purple in color and weighed 14 g. On histologic evaluation, the tumor demonstrated focal vascular invasion, consistent with parathyroid carcinoma (Figure 1). Otherwise, the tumor capsule was intact, all margins were negative including the inferior portion of the left thyroid lobe. The left superior parathyroid gland was biopsied and reported to be normal parathyroid tissue on histological analysis. Six level VI lymph nodes were analyzed and negative for tumor. Intra-operatively, iPTH fell to 41 ng/L (41 pg/mL) and post-operatively it fell to 14 ng/L (14 pg/mL) and she had a calcium nadir of 1.7 nmol/L (6.8 mg/dL). She was started on cholecalciferol, calcitriol and calcium supplementation in the immediate post-operative period. She was persistently hypocalcemic despite calcium supplementation until postoperative day 4 when her calcium normalized. Renal ultrasound was negative for nephrocalcinosis, calculi or hydroureteronephrosis, and pelvic ultrasound was negative for uterine tumors. The patient underwent a skeletal survey that demonstrated cystic changes to the left femoral neck requiring further evaluation. There was no suspicion for jaw tumors. MRI of the left hip without contrast demonstrated a multi-lobulated cystic lesion within the proximal left femoral neck involving nearly 50% of the diameter of the femoral neck consistent with a brown tumor (Figure 2). The patient was made non-weight bearing to the left lower extremity, and was discharged on postoperative day 5 in good condition.

Figure 1:

H&E and immunohistochemistry stains.

(A) Photomicrograph of parathyroid carcinoma showing scattered atypical cells and focal intervening fibrous bands (H&E). (B) Photomicrograph showing vascular invasion (H&E). Arrow points to vascular invasion. (C) CDC31 immunohistochemistry showing vascular invasion. Arrow points to vascular invasion.

Figure 2:

Brown tumor to the left femoral neck.

(A) MRI of the hip on coronal plane showing a multilobulated cystic lesion occupying more than 50% of the left femoral neck. Arrow points to a brown tumor. X-ray views showing thickening of the trabeculae and a well-defined lucency to the medial aspect of femoral neck on post-operative week 1 (B), and 6 months later (C). Arrows point to a brown tumor.

The patient has been followed in the otolaryngology, endocrinology and orthopedic surgery clinics postoperatively and is doing well. Calcium levels normalized to 2.15 mmol/L (8.6 mg/dL) when checked on postoperative day 16; calcitriol was discontinued by 2 months’ post-operatively once serum calcium levels improved, iPTH remains in the normal range and there is no hypercalcemia on calcium and cholecalciferol supplementation at 6 months’ post-operatively. Her left femoral brown tumor has significantly improved on X-rays (Figure 2) and her weight bearing has progressed to crutch use only outside of the home. Unfortunately, her scoliosis has progressed from 59 degrees at time of presentation to 63 degrees 6 months later, and thus she underwent posterior spinal fusion from T4 to L2 per orthopedics recommendation. Otherwise, her bone pain has essentially resolved and she remains disease-free.

Discussion

We describe the case of a 14-year-old female with parathyroid carcinoma that constitutes the first pediatric case with a reported HRPT2/CDC73 mutation, c.70 G>T, which has only been described as a somatic mutation in two adult cases before [16], [17]. Parathyroid carcinoma in the pediatric population is a rare entity; to date, only nine previous cases have been reported in children under 16 years of age [2], [8], [9], [10], [11], [12], [13], [14], [15], affecting children ranging from 8 to 15 years of age (Table 1). Most previous cases were sporadic parathyroid carcinomas, except for two. The first one was a 14-year-old male reported by McHenry et al. that presented with a hypercalcemic crisis in the context of familial hyperparathyroidism. The second case was reported by Hamill et al., of an 8-year-old female with family history of primary hyperparathyroidism suggesting a genetic predisposition [2], [8], [9], [10], [11], [12], [13], [14], [15].

Patients with parathyroid carcinoma have markedly elevated calcium levels above 3.5 mmol/L (14 mg/dL), or 3–4 mg/dL (0.85–1 mmol/L) above the upper limit of normal, in contrast to patients with parathyroid adenoma. For the reported pediatric cases, including ours, average total calcium at presentation is 3.8 mmol/L (15.1 mg/dL, reference range, 8.4–10.2 mg/dL) [2], [8], [9], [10], [11], [12], [13], [14], [15]. This severe hypercalcemia is generally associated with presenting symptoms of fatigue, weakness, weight loss, anorexia, polyuria, polydipsia, renal colic, and bone pain. Additionally, patients with parathyroid carcinoma present with extremely high iPTH levels, generally 3–10 times above the upper limit of normal.

A palpable neck mass is a remarkably rare finding in parathyroid adenoma, but has been associated with up to 76% of cases of parathyroid carcinoma [18], [19]. Of the nine reported cases of pediatric parathyroid carcinoma with a reported physical exam (one of them did not report it), a clinically palpable neck mass was found in seven patients, equivalent to an incidence of 77.8% in children <16 years old [2], [8], [9], [10], [11], [12], [13], [14], [15]. Higher-resolution anatomical studies such as computed tomography (CT) or magnetic resonance imaging (MRI) are of significant value in the preoperative evaluation when malignancy is suspected, as they provide details on the location of the lesion and its relation to other structures, as well as reveal invasion of surrounding structures and enlarged lymph nodes [19].

Our patient became significantly hypocalcemic down to 1.7 mmol/L (6.8 mg/dL) on post-operative day 1, and was symptomatic, with numbness and tingling to her face and legs as well as a positive Chvostek sign. She required intravenous calcium and calcitriol supplementation. Her phosphorus was as low as 0.7 mmol/L (2.0 mg/dL) the first day post-operatively, and then remained normal until 1 month after surgery when it started to rise, to a peak of 2.0 mmol/L (6.1 mg/dL) 2 months’ post-operatively and was still elevated at 5 months. She required calcitriol supplementation for 2 months after tumor removal and calcium supplementation still at 6 months after surgery. Her post-operative hypocalcemia, even though confounded by hungry bone syndrome and vitamin D deficiency, is most likely explained by chronic suppression of the three remaining parathyroid glands in the face of chronic hyperparathyroidism.

To our knowledge, this is the first case documenting parathyroid carcinoma in a child presenting with SCFE. While the link between primary hyperparathyroidism and reduced bone mineral density with cortical bone disease is well established in adults [20], there have only been 10 pediatric case reports worldwide linking primary hyperparathyroidism and SCFE [21], [22], [23], [24], [25], [26], [27], [28], [29], [30]. Our patient presented initially with SCFE and was found after full skeletal survey to have a cystic lesion to the left femoral neck osteitis fibrosa cystica. With an incidence of 10.8 per 100,000 children, SCFE is the most common hip disorder affecting children and adolescents, usually in obese patients between the ages of 8 and 15 years [31], [32], [33], [34]. However, the vast majority of children with SCFE do not have hyperparathyroidism or parathyroid carcinoma.

Even with early consideration of parathyroid carcinoma, the diagnosis is a difficult one to make, and often is not suspected until the tumor is visualized by the surgeon. In about 50% of cases, parathyroid carcinomas are surrounded by a dense, fibrous, grayish-white capsule that adheres tenaciously to adjacent tissues and makes the tumor difficult to separate from contiguous structures [18]. Adhesions are partly due to a desmoplastic reaction, which is a reactive stromal response that creates a dense fibrotic tissue surrounding the tumor [35]. Thus, a firm, lobulated, or fixed tumor that is adherent to surrounding structures should alert the surgeon to a possible malignant diagnosis [18].

Once the diagnosis is suspected, complete en bloc resection of the tumor and surrounding neck structures should be performed [2], [36]. In adults, successful en bloc resection of the tumor results in 90% long-term survival, while incomplete tumor resection has been shown to have a local recurrence rate of 50% with a mortality rate of 46% [37], [38]. Due to its short half-life, intra-operative PTH measurement accurately predicts the outcome of parathyroidectomy [39].

In 2002, the gene CDC73 (formerly known as HRPT2), encoded in chromosome 1q25, and its corresponding protein parafibromin were identified [40], and mutations in this tumor suppressor gene have been found to be associated with cases of sporadic parathyroid carcinoma, autosomal dominant hyperparathyroidism-jaw tumor syndrome (HPT-JT), and familial isolated hyperparathyroidism (FIHP). Up to 70% of sporadic cases of parathyroid carcinoma are found to have HRPT2/CDC73 mutations [17], [40], [41], [42], [43], as opposed to <2% of cases of parathyroid adenoma [44]. HRPT2/CDC73 encodes the 531 amino acid protein parafibromin (parathyroid disease and fibro-osseous lesions), which is the human homologue of yeast CDC73. Parafibromin is located in the nucleus and is part of the complex that contains the human homologues of the yeast Paf1 complex (hPaf1). Parafibromin acts as a tumor suppressor and is involved in transcription regulation, histone modification, RNA processing and cell proliferation [16], [45]. It has been shown that parafibromin down-regulates the expression of the oncogene cyclin D1 [46] and that increased expression of cyclin D1 is associated with the formation of parathyroid adenomas and carcinomas [42].

Our patient was found to be heterozygous for a germline mutation in HRPT2/CDC73 (c.70 G>T, p. Glu24Ter), which is located in exon 1, and is predicted to cause loss of normal protein function by creating an early stop codon, E24X. In a review by Newey et al., among patients with HPT-JT syndrome, FIHP, parathyroid carcinoma, parathyroid adenoma and sporadic ossifying fibromas of the jaw, mutations in exon 1, 2 and 7 were overrepresented, even after adjusting for exon size, accounting for 34, 17 and 21%, respectively [47]. The author also reviewed that there had been 111 mutations to HRPT2/CDC73 reported as of 2008, 68 germline and 38 somatic [47]. Most mutations to HRPT2/CDC73 are frameshift, nonsense, and missense; however, as many as 35% of patients with HPT-JT have deletions of HRPT2/CDC73 and it is recommended that deletion analysis of the HRPT2/CDC73 gene via MPLA (multiplex ligation-dependent probe amplification) be performed in patients with parathyroid carcinoma who do not have HRPT2/CDC73 point mutations detected by sequencing [48], [49]. The same patient may have both germline and somatic mutations or two different somatic mutations to HRPT2/CDC73, and this explains why patients with a germline mutation can have asynchronous parathyroid neoplasms, consistent with the Knudson ‘two hit’ concept of biallelic inactivation of tumor suppressor genes, such as HRPT2/CDC73 [17], [50]. The 70 G>T mutation has been reported previously as a somatic mutation in two adult patients with sporadic parathyroid carcinoma [16], [17]; however, to our knowledge it has not been reported as a germline mutation and it is also the first HRPT2/CDC73 mutation reported in a pediatric case of parathyroid carcinoma.

The finding of unexpected germline mutations in apparently sporadic parathyroid carcinomas has already been reported by other authors, and as these cancers may represent an occult form of HPT-JT, clinical monitoring for jaw tumor and kidney lesions is advised and gene testing of family members is suggested, with monitoring of serum calcium in gene carriers [17], [43]. The HRPT2 protein product parafibromin is being investigated as an immunohistochemical marker for parathyroid carcinoma [41]. Cetani et al. [16] found that loss of parafibromin staining had a sensitivity of 100% and a specificity of 88%, compared to 82% sensitivity and 96% specificity for HRPT2/CDC73 mutation. The author recommends that both HRPT2/CDC73 gene testing and parafibromin staining should be done in the context of parathyroid tumors with atypical features. Wang et al., in turn, reported that combination of both markers had a sensitivity of 92.3% without reduction in specificity, which was 100% for HRPT2/CDC73 mutations and 95% for loss of parafibromin expression [51]. Using genetic testing for HRPT2 mutations and staining for parafibromin is especially helpful considering that parathyroid carcinoma is particularly difficult to diagnose pathologically: in a large study of 40 parathyroid carcinomas defined based on recurrence and metastasis rather than by pathological criteria alone, less than half were correctly diagnosed as malignant at presentation based on the combined clinical and pathological findings [52].

While parathyroid carcinoma is an exceedingly rare entity amongst the pediatric population, it is an important diagnosis that should be considered by healthcare providers when a patient presents with hyperparathyroidism and a palpable neck mass. Serum calcium level is the most reliable indicator of disease recurrence [39]. Close follow-up is required during the first 2 years after surgery because of the higher rate of recurrence during this period; however, long-term follow-up is recommended because recurrence can happen up to 15 years after surgery [52]. In patients with HRPT2/CDC73 mutations, Witteveen et al. reported a seven-fold increased risk of developing local or distant metastasis. All four patients with the gene mutation developed local recurrence and/or distant metastasis, which occurred only in 10 of 19 patients without mutations [53]. Wang et al. did not find a significant correlation between a mutation in HRPT2/CDC73 and distant metastases but did find a higher incidence of recurrence in patients with HRPT2/CDC73 mutations (100% vs. 50%, p=0.031), after adjusting for gender, age, initial serum calcium and duration of follow-up [51].

In conclusion, parathyroid carcinoma is rare in pediatrics but should be considered in a patient with hypercalcemia and a neck mass. We report the first pediatric patient with a HRPT2/CDC73 mutation in the context of parathyroid carcinoma. Genetic screening for HRPT2/CDC73 mutations is prudent in pediatric patients with parathyroid carcinoma. Close follow-up is required for patients who carry this mutation due to a higher risk of metastasis and recurrence. Screening of family members for this mutation may be necessary.