Oxalate Nephropathy in a patient with Neuroendocrine tumor receiving Long-acting Octreotide

Peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTA-TATE along with long-acting Octreotide is an established treatment for metastatic neuroendocrine tumours (NETs). Renal dysfunction following PRRT is usually attributed to radiation-induced nephrotoxicity. A 55-year-old man with metastatic somatostatin receptor-positive NET, diagnosed in April 2023, initially received long-acting octreotide, external beam radiotherapy, and six cycles of etoposide chemotherapy. Persistent disease on Ga-68 DOTA-TATE PET imaging in November 2024 prompted treatment with four cycles of ¹⁷⁷Lu-DOTA-TATE PRRT between February and December 2025, along with monthly long-acting octreotide injections. Baseline renal function was normal and remained stable at a serum creatinine of 0.9 mg/dL till December 2025. He was referred to nephrology in March 2026 with an asymptomatic rise in serum creatinine to 2.3 mg/dL. Evaluation revealed subnephrotic proteinuria (820 mg/day), normal-sized kidneys, bland urinary sediments. PRRT-related nephrotoxicity and acute interstitial nephritis were initially considered. Kidney biopsy demonstrated extensive tubular calcium oxalate crystal deposition along with acute interstitial inflammation. In the absence of other identifiable causes of enteric hyperoxaluria, octreotide-induced pancreatic exocrine insufficiency was suspected as the most likely aetiology. The patient received a short course of corticosteroids in view of interstitial inflammation in the biopsy. Serum creatinine declined to 1.5 mg/dL on follow-up. Early recognition is critical, as progressive renal dysfunction may compromise eligibility for PRRT, a cornerstone treatment for NETs.