6634 Dual-Mediated PTH And Osteolytic Hypercalcemia In Metastatic Endometrial Carcinoma

Abstract Disclosure: C.K. Persaud: None. D.J. Beckman: None. Background: Hypercalcemia of malignancy occurs in 20-30% of advanced stage cancer patients. Etiologies include parathyroid hormone-related peptides (PTHrP)-mediated, osteolytic metastases-mediated, overproduction of 1,25-dihydroxycholecalciferol, and rarely parathyroid hormone (PTH)-mediated. PTH-mediated hypercalcemia of malignancy is rare and occurs through ectopic PTH production or primary hyperparathyroidism. We report a rare case of both PTH-mediated and osteolytic-mediated hypercalcemia in the setting of malignancy. Clinical Case: A 57-year-old female with history of endometrial cancer and multiple solid organ metastasis, presented with two weeks of progressive poor oral intake, nausea, emesis, and right flank pain. On hospital admission, she had a serum calcium of >20.1 mg/dL (8.6-10.2), PTH of 203 pg/mL (15.0-65.0), and creatinine of 1.7 mg/dL (0.7-1.2, baseline 1.3). Non-contrasted CT chest/abdomen/pelvis noted increased size of known right adrenal metastasis, new left adrenal metastasis, periaortic lymphadenopathy, and scattered nodules in the subcutaneous tissues of the abdomen and chest, however bone metastasis were not noted. Patient’s hypercalcemia was treated with zoledronic acid, calcitonin, cinacalcet, and eventually denosumab due to difficulty controlling hypercalcemia. Additional labs obtained during evaluation included ionized calcium >2.5 nmol/L (1.12-1.32), PTHrP <2.0 pmol/L (<2.0), 1,25-dihydroxycholecalciferol <10 pg/mL (21-65). Patient’s right adrenal metastasis biopsy one month prior to admission was subsequently stained for PTH and was negative. Technetium-99m sestamibi scan was obtained for localization of parathyroid adenoma or carcinoma. The scan did not localize, however did show numerous new lytic lesions in the skull, spine, sternum, rib cage, and right humerus. Patient’s hospital course was complicated by progressively worsening renal function, anemia, and thrombocytopenia. Patient was discharged to a long-term acute rehab facility off hypercalcemia treatment with a corrected calcium of 10.0 mg/dL. Conclusion: PTH-mediated hypercalcemia is a rare cause of hypercalcemia of malignancy. PTH levels are typically low or low-normal in osteolytic mediated hypercalcemia. Generally, if PTH is elevated in hypercalcemia, an alternate etiology is not evaluated. This case highlights a rare dual-mediated hypercalcemia of malignancy. The patient’s PTH level elevation was discordant with her high degree of hypercalcemia and prolonged treatment course. She was subsequently found to have widespread bone metastases contributing to hypercalcemia. While multiple etiologies of hypercalcemia can be rare, it is important to evaluate for all contributing causes, especially with additional clinical conditions, such as malignancy. Presentation: 6/3/2024