THU525 Atypical Presentation Of Parathyroid Carcinoma In The Lungs

Disclosure: J.N. Jacinto: None. O. Reyes: None. M. Cating-Cabral: None. R. Santiago: None. J. Andal: None. A 66-year-old female with a history of parathyroid adenoma underwent partial parathyroidectomy and thyroidectomy of the right lobe in 2006. She has the following comorbidities: pre-diabetes, hypertension, multiple liver cysts, medullary nephrocalcinosis and nephrolithiasis, ureterolithiasis and uterine intramural myoma. She also has a strong familial disposition of endocrine tumors. During the last quarter of 2018, parathyroid hormone and calcium levels were elevated and parathyroid imaging revealed an adenoma on the posteromedial aspect of the left thyroid lobe. Removal of the adenoma was offered but insisted on medical treatment. In 2022, she was admitted for subarachnoid hemorrhage due to fall. There was an incidental finding of a lung mass with minimal pleural effusion on the right lung lobe. PET-scan revealed five FDG-avid nodules (SUV up to 9.6) with the largest in the right middle lobe measuring 2 x 2 x 2 cm. Percutaneous needle biopsy was performed which showed a tumor with fairly uniform cells in organoid nests and solid clusters. By immunohistochemistry (IHC), the tumor cells were diffusely and strongly positive for CK and GATA-3; focally positive for chromogranin and synaptophysin; and negative for TTF-1, Pax-8, and S100. This was signed out as an epithelial tumor with neuroendocrine features; the differential diagnosis includes pulmonary neuroendocrine tumor versus metastasis from the prior parathyroid lesion. She subsequently underwent completion thyroidectomy and video-assisted thoracoscopic surgery. The lung wedge resections both showed tumors with similar morphology and IHC staining pattern as the biopsy. Additional stains were also performed to rule out other entities, which were all negative (CK7, CK20, CD56, mammaglobin, GCDFP-15, TTF-1, S100, ER, Pax-8, HSA, and SALL-4). The Ki-67 proliferation index was 17.26%. Because the overall findings were not definitive, comprehensive genomic profiling by next generation sequencing (NGS) was recommended and subsequently performed. NGS showed gene alteration in CDC73, with a variant allele frequency of 50%; this finding has been documented in parathyroid carcinoma. Pre-operative parathyroid hormone levels remained unchanged (408 to 397 pg/ml) despite surgery. Currently, there is no available targeted therapy to address her genomic alteration. Hyperparathyroidism-jaw tumor syndrome was entertained. The multidisciplinary team advised en-bloc resection of the lung tumor and additional gene testing for family members. She opted for palliative care and is on cinacalcet for her hyperparathyroidism. Presentation: Thursday, June 15, 2023