ODP627 Hypercalcemia in a Patient With Gastrointestinal Stromal Tumor (GIST): Evaluation and Treatment Strategies

A 52-year-old African woman was found to have a pelvic mass at the age of 41. Following resection of small bowel tumors at the time, she was diagnosed with GIST and peritoneal metastases were confirmed. Despite treatment with imatinib, her disease progressed and was started on regorafenib. Due to lack of consistent insurance coverage, she took this medication intermittently for several years, and her tumor progressed to develop intra-abdominal peritoneal and pelvic metastases. She underwent debulking surgery, and her disease subsequently remained stable with regorafenib. Unfortunately, she developed hemoptysis which led to discontinuation of regorafenib, and while off treatment, the patient developed altered mentation, extreme lethargy, and poor PO intake. She was found to have a serum calcium of 16 mg/dL and was admitted for treatment of severe hypercalcemia. With intravenous (IV) fluids, calcitonin and zoledronic acid, her calcium improved to 11-12 mg/dL; however, despite additional therapies, including denosumab and repeat zoledronic acid, her calcium did not normalize. Further evaluation revealed: 25-hydroxy-vitamin D3 level 22.2 ng/mL (normal), 1,25-dihydroxy-vitamin D3 107 mcg/mL (elevated), PTH 6. 0 pg/ml (low), and PTHrP 3.3pmol/L (low). She was given a diagnosis of calcitriol-mediated hypercalcemia and started on IV hydrocortisone 100 mg every 12 hours. Her serum calcium started to improve within 48 hours and normalized after eight days to 9.8mg/dL. Her clinical condition improved, and she was discharged with prednisone 20 mg daily. At the time of her post-hospital follow up several days later, her serum calcium remained normal. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.