Abstract Disclosure: N. Sekhon: None. R.J. Bingham: None. Background: We present a challenging diagnostic case of a 73-year-old female with PTH-mediated hypercalcemia in the presence of new metastatic uterine cancer. Case: A 73-year-old female with a past medical history of hypertension and abdominal aortic aneurysm was seen in the hospital for hypercalcemia. She endorsed constipation, fatigue, and generalized weakness for the past few weeks. This was the second hospitalization related to hypercalcemia over the period of 10 days. During the previous hospitalization, her admission calcium was 17 mg/dL and was treated with IV fluids, calcitonin, and zoledronic acid. There was a history of intentional weight loss of about 30-40 lbs in the last 3 months by reducing carbohydrate intake. The patient had a 40-pack years of smoking history. There was no family history of calcium disorders or cancers. Home medications included amlodipine 10 mg QD, docusate sodium 100 mg BID, senna 1 tab QHS, and Vit D 5000 U QD. On physical examination, she was hemodynamically stable but appeared confused and lethargic. The rest of the examination was unremarkable. Laboratory results were remarkable for hypercalcemia (Ca: 13.3 mg/dL), hypophosphatemia (Phosphorus: 2.3 mg/dL), and elevated PTH of 418.3 pg/mL (Ref. Range: 18.4-80.1 pg/mL). CT abdomen/ pelvis revealed innumerable ill-defined hypodense lesions throughout the liver concerning metastatic disease and a 5 cm mass in the uterine fundus. The patient was worked up with the view of hypercalcemia related to malignancy. However, PTHrP (PTH-related peptide) came back normal, which was checked twice during both hospitalizations. Liver biopsy showed metastatic high-grade carcinoma highly suspicious for GYN malignancy with negative PTH staining. Imaging studies for localization including CT soft tissue neck and CT 4D parathyroid with and without contrast failed to show any parathyroid lesions. Endometrial biopsy obtained during subsequent hospitalization showed high-grade adenocarcinoma with focal squamous differentiation. Immunohistochemical staining identified scattered positivity for PTH. The patient was managed as per hypercalcemia of malignancy guidelines with IV fluids and denosumab. Discussion: Hypercalcemia of malignancy due to ectopic PTH secretion has been reported in < 1% of cases. Only two endometrial cancer cases with ectopic PTH have been reported in the literature. PTH-mediated hypercalcemia is seen in primary hyperparathyroidism, parathyroid cancers, or ectopic PTH. In all cases of hypercalcemia of malignancy, primary hyperparathyroidism should be ruled out in the presence of elevated PTH. Diagnosing ectopic PTH secretion by tumor can be challenging due to constant changes in cells with metastasis. Conclusion: This is a rare case of endometrial cancer with liver metastasis and ectopic PTH secretion by primary tumor leading to recurrent hospitalizations related to hypercalcemia. Presentation: 6/2/2024
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