7187 Non-islet Cell Tumor Hypoglycemia in a Patient With Metastatic Renal Cell Carcinoma

Abstract Disclosure: G.W. Bao: None. A.Y. Yin: None. We report a rare case of non-islet cell tumor hypoglycemia (NICTH) in a patient with metastatic renal cell carcinoma. NICTH is a paraneoplastic syndrome due to increased production of an incompletely processed form of insulin-like growth factor 2 (“big IGF-2”). It requires a high-level of suspicion for diagnosis and is challenging to manage. Our patient is a 69 year old gentleman with a history of deceased donor renal transplant in 1994 and 2008. He was diagnosed with renal cell carcinoma (RCC) metastatic to bone, lymph nodes, and lungs, which was initially treated with cabozantinib, later switched to lenvatinib and everolimus due to disease progression. On admission, he presented with anasarca and weakness. He had recurrent fasting hypoglycemia associated with confusion and lethargy. The lowest serum glucose was 28 mg/dL. He was also diagnosed with primary hypothyroidism (TSH 25.1 uIU/mL and free T4 0.31 ng/dL), suspected to be due to tyrosine kinase inhibitor therapy. Levothyroxine was initiated. Cosyntropin stimulation resulted in a post-stimulation cortisol of 7 ug/dL, although this was felt not to be reliably diagnostic of adrenal insufficiency in the setting of profound hypoalbuminemia. IGF-1 and IGF-2 were 16 ng/mL and 388 ng/mL, respectively; IGF-2: IGF-1 ratio was 24.3. He was treated with intravenous dextrose and prednisone 30mg daily with stabilization of glucoses for a few days. On hospital day 19, he acutely decompensated and passed away shortly after being transitioned to comfort-focused care. Non-diabetic hypoglycemia is relatively uncommon, and may be seen in patients with liver disease, sepsis, adrenal insufficiency, and malignancy. We report a case of NICTH in a patient with metastatic RCC, which is a particularly rare cause of hypoglycemia. NICTH is due to tumor production of “big IGF-2”, a precursor of IGF-2, which mimics the effects of insulin and causes fasting hypoglycemia. NICTH is more commonly associated with mesenchymal and epithelial tumors such as fibromas, fibrosarcomas, and hepatocellular carcinomas. NICTH due to RCC appears to be a much more rare entity, with as few as four cases reported in the literature. Laboratory findings of NICTH include low insulin, pro-insulin, C-peptide, and β-hydroxybutyrate during hypoglycemia. An IGF-2: IGF-1 ratio >10 is considered virtually diagnostic. Surgical excision is curative, although often delayed or not feasible, and patients frequently require intravenous dextrose. High-dose steroids (ie, prednisone 30-60mg daily) can be used, which promotes “big IGF-2” clearance. NICTH is likely under-recognized in patients with advanced malignancies. This diagnosis should be considered in those with refractory hypoglycemia, although management is challenging if tumor control cannot be achieved. Presentation: 6/1/2024