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Abstract: PO1865

A Rare Case of Calcitriol-Mediated Hypercalcemia in Metastatic Gastrointestinal Stromal Tumor (GIST)

Session Information

Category: Onco-Nephrology

  • 1500 Onco-Nephrology

Authors

  • Khan, Iman Sajid, Weill Cornell Medicine, New York, New York, United States
  • Gutgarts, Victoria, Memorial Sloan Kettering Cancer Center, New York, New York, United States
  • Kirchhoff, Daniel, Memorial Sloan Kettering Cancer Center, New York, New York, United States
  • Ramanathan, Lakshmi V., Memorial Sloan Kettering Cancer Center, New York, New York, United States
  • Shingarev, Roman A., Cleveland Clinic, Cleveland, Ohio, United States
Introduction

Hypercalcemia accompanies 10-30% of malignancies. Calcitriol production accounts for <1% cases, usually with lymphoma, but has been reported with solid tumors.

Case Description

A 62 year old male with GIST with liver involvement was admitted for an elevated calcium (Ca) of 13.9 mg/dL & AKI with creatinine (Cr) 2.2 mg/dL. Diagnosed with GIST 3 years prior, he was treated with imatinib & an investigational mitogen-activated protein kinase enzyme inhibitor. Due to disease progression, he was switched to sunitinib 1 week prior to admission and endorsed taking 100,000 IU of OTC vitamin D tablets daily for perceived immunologic benefits.
Further workup showed bland urinalysis & fractional sodium excretion of 2.6%. Renal sonogram was normal. AKI was ascribed to hypercalcemia-mediated vasoconstriction & renal blood flow reduction. He had an ionized Calcium 6.6 mg/dL (nl: 4.8-5.3 mg/dL), appropriately low PTH & PTHrP 0.9 pmol/L (nl ≤4.2 pmol/L). The 25(OH) vitamin D was reported at >156 ng/mL, then quantified at 240 ng/mL. Calcitriol was elevated at 71 pg/mL (nl: 18-64 pg/nL). Etiology of hypercalcemia was thought to be from excess vitamin D intake. Cr & Ca improved with hydration, calcitonin & pamidronate. He was readmitted with recurrent hypercalcemia, persistently high 25(OH) vitamin D & calcitriol. Suspected to be tumor-mediated, prednisone was added to suppress conversion of 25(OH) vitamin D to calcitriol. Over a 3-week prednisone taper, Ca, Cr, 25(OH) vitamin D, calcitriol normalized.

Discussion

In kidneys, 1 alpha hydroxylase converts 25(OH) vitamin D to calcitriol causing Ca retention. This occurs autonomously in lymphomas & granulomatous diseases causing hypercalcemia. Our case is unique as it (a) describes calcitriol mediated hypercalcemia associated with GIST, (b) highlights that hypercalcemia in malignancy can be multifactorial & in our case was from excess vitamin D intake & elevated calcitriol levels.

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