8126 PTH-Independent, Calcitriol-Mediated Hypercalcemia In Renal Cell Carcinoma

Abstract

Abstract Disclosure: G.K. Rai: None. A. De Rosairo: None. K. Madani: None. D. Sacoto: None. A.A. Franco-Akel, MD: None. R. Belokovskaya: None. Hypercalcemia of malignancy is a known complication of advanced cancer. It occurs through various mechanisms, one of which is via 1,25-dihydroxyvitamin D (calcitriol). Calcitriol-mediated hypercalcemia accounts for approximately 1% of cases of hypercalcemia in the setting of malignancy and is usually seen in lymphomatous solid tumors. We present a gentleman with clear cell renal cell carcinoma associated with hypercalcemia with normal levels of intact parathyroid hormone (PTH), PTH-related protein (PTHrP), and 25-hydroxyvitamin D but elevated calcitriol levels. A 48 year-old-male with no significant past medical history with complaints of fatigue, hematuria, and weight loss of 38 pounds in 3 months was following urology for an elective right-sided nephrectomy. MRI of the abdomen and pelvis found a 16.1 cm renal mass with necrotic areas, causing mass effects on the liver, pancreas, and IVC. Preoperative laboratory showed hypercalcemia of 13.7 mg/dL (corrected 13.9 mg/dL) with microcytic anemia (hemoglobin 8.8 g/dL, MCV 72 fl). Workup showed low iPTH (3 pg/dL), 25-hydroxyvitamin D (16.9 ng/dL), and phosphorus level (1.7mg/dL) with elevated calcitriol (94.3 pg/dL) and a normal PTHrP. CT chest showed multiple pulmonary nodules on bilateral lobes, with the largest nodule ∼ 4.5 mm. Hypercalcemia was managed with IV fluids, calcitonin 300 units Q12 for two days, Denosumab IV infusion, prednisone 60 mg for three days, and oral ergocalciferol 50,000 units weekly. Calcium levels normalized, after which the patient underwent nephrectomy. Pathology revealed renal cell carcinoma grade G4 with mixed features of clear cell carcinoma with sarcomatoid and rhabdoid features. We report an incidental finding of hypercalcemia in a patient with renal mass. The elevated calcitriol levels can be attributed to ectopic calcitriol production through the renal mass. Post nephrectomy calcium levels remained within normal range for consecutive weeks. With this, we concur that hypercalcemia most likely originated from the renal mass that had ectopic production of calcitriol. Dysregulated calcitriol production is a well-known complication of lymphomas and granulomatous disease but is seldom reported with solid tumors. Usually, the etiology for hypercalcemia in patients with renal cell carcinoma is the overproduction of PTHrP, which was not the case with our patient. The ultimate resolution of hypercalcemia of malignancy was attained by treating the underlying malignancy. Presentation: 6/1/2024