PMC8842631_01
(A) Original histology showing the main mass (arrow) and tumoral nests (*) that extend into the adipose tissue. This invasion, together with vascular invasion, mitotic figures, and necrosis is indicative for a low-grade parathyroid carcinoma (hematoxylin & eosin staining, 40X). (B, C) Cervical computed tomography demonstrating a right retro-tracheal mass of 15.9 x 12.9 x 7.5 mm corresponding to local recurrence of the incompletely resected parathyroid carcinoma.
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Review of the original surgical pathology at our institution led to the conclusion that the tumor was in fact a parathyroid carcinoma ( Figure 1A ). Imaging with fluorocholine (18FDG) PET/CT revealed a right retro-tracheal mass suggestive for residual/recurrent local disease ( Figures 1B, C ), a hypermetabolic left cervical lymph node that ultimately showed a benign cytology, and no evidence for distant metastasis.
(A) Calcium levels under therapy with denosumab. ZA, zoledronic acid; CAL, calcitonin; D60, denosumab 60 mg; D120, denosumab 120. (B) Selected PTH, phosphate and creatinine levels. PTH, parathyroid hormone.
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Although denosumab is not officially approved for the control of hypercalcemia in Switzerland, it was introduced with an initial dose of 120 mg, followed by eight doses of 60 or 120 mg ( Figure 2A ). Selected additional biochemical markers such as phosphate levels are summarized in  Figure 2B .