SAT205 (99)Technitiumm Sestamibi Negative Sporadic Metastatic Parathyroid Carcinoma In A Young Female-A Diagnostic Conundrum

Disclosure: D.V. Reddy: None. S. Paidipally: None. V. kyatham: None. S. Palle: None. C. Bhandiwad: None. Background: Parathyroid carcinoma (PC) is a very rare and indolent endocrine malignancy occurring a decade earlier than parathyroid adenoma. It can present as recurrent pancreatitis, anemia, and peptic ulcers. Serum calcium >14mg/dl, 3-10 times ULN of PTH, and concomitant renal and bone involvement should arise suspicion for PC. PC is diagnosed only through histopathology in the majority. It can also present during a prolonged follow-up, either by local recurrences or distant metastases. Clinical Case: A 27 year old female presented with hypercalcemic crises (as pancreatitis). At admission serum calcium and PTH were grossly elevated; 15.1 mg/dl (8.5-10 mg/dl) and 363 pg/ml (10-55 pg/ml) respectively. Abdominal CT revealed acute pancreatitis with medullary nephrocalcinosis. Ultrasonography of the neck revealed a colloid cyst in the right lobe of thyroid.(99)Tc m-sestamibi /SPECT-CT revealed no uptake. CT neck and chest showed a 13 mm X 13 mm well-defined round nodular lesion in the left apico-posterior segments of the lung. 18F-FDG PET/CT revealed uptake in the lesion with an SUV max of 10, suggestive of a metabolically active solitary pulmonary nodule. She had a similar presentation 8 years back and was diagnosed to have parathyroid adenoma for which she underwent resection. Serum PTH and calcium levels normalized postoperatively and also on follow-up till 3 years. Differentials include-recurrent ectopic parathyroid adenoma, parathyromatosis, and metastatic parathyroid carcinoma. After managing hypercalcemia medically, the patient underwent video-assisted thoracoscopic surgery with left lung wedge resection. Postoperatively serum calcium and PTH normalized. Histopathology revealed a grey-white nodule of 1.4X1.5X1.2 cm with sections, showing a well-defined lesion composed of lobules and nests of tumor cells separated by thin-walled vascular sinusoids. Tumor cells were polygonal with well-defined margins, moderate granular cytoplasm, and vesicular nuclei showing prominent nucleoli with a mitotic activity of 9/hpf. Immunohistochemistry revealed staining with PanCK, GATA3, and S100 with focal PAX 8 activity in the periphery. MIB index was 18%.IHC was suggestive of a neuroendocrine tumor consistent with metastatic parathyroid carcinoma. Whole exome sequencing did not reveal any pathogenic variants. Conclusion: Though (99)Tc MIBI is useful in localizing PC, there are reports of false negative MIBI in documented cases of PC, which has been ascribed to the defective transport to the interior of the malignant cells. This demonstrates the importance of a multimodality imaging approach in such cases. (99)Tc MIBI may miss certain cases of PC substantiating the importance of 18F-FDG PET/CT in diagnosis as well as follow-up. Reference: Evangelista L et al. FDG-PET/CT and parathyroid carcinoma: Review of literature and illustrative case series. World J Clin Oncol 2011; 2(10): 348-354. Presentation: Saturday, June 17, 2023