Complete Molecular Response of Left Adrenal Metastasis from Pancreatic Neuroendocrine Tumor Following SBRT: A Case Report

Abstract

Background: While pancreatic neuroendocrine tumors (PNETs) often metastasize to the liver, adrenal gland involvement is uncommon. Management of adrenal metastases with stereotactic body radiation therapy (SBRT) is not common and outcomes are not well described. We report a case of metastatic PNET to the adrenal gland demonstrating sustained complete molecular response without anatomic resolution following SBRT within a multimodal treatment.

Case Description: A 48-year-old male patient was diagnosed in September 2023 with a well-differentiated grade 1 PNET. Initial imaging revealed an 8.9 cm centrally necrotic pancreatic tumor with diffuse peripancreatic infiltration and a biopsy proven 2.9 cm left adrenal metastasis. The tumor was somatostatin receptor (SSTR) positive (Krenning Score 4) and was deemed surgically unresectable. Despite sequential treatment with capecitabine-temozolomide, FOLFOX (5-FU, Leucovorin, and Oxaliplatin) and FOLFIRI (5-FU, Leucovorin, and Irinotecan), the adrenal lesion progressed, enlarging to 6.9 × 6.3 cm and demonstrated high-grade transformation to well-differentiated grade 3 (Ki-67 40%) by May 2025. The patient underwent SBRT to the left adrenal metastasis, receiving a total dose of 6,000 cGy in 5 fractions followed by systemic peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE for primary pancreatic disease control. One month after SBRT, post-treatment imaging demonstrated reduction in adrenal lesion size (4.5 × 4.0 cm) with complete absence of radiotracer uptake. Follow-up imaging in December 2025 confirmed continued size reduction and persistent absence of SSTR uptake. At nearly one-year post-SBRT, a repeat ⁶⁴Cu-DOTATATE PET/CT scan showed no left adrenal gland hypermetabolic activity consistent with a sustained complete molecular response despite persistent residual lesion size.

Conclusions: This case of metastatic PNET to the left adrenal gland achieved complete molecular response without anatomic resolution nearly one-year following ablative SBRT within a multimodal treatment strategy. SBRT may represent an effective local control strategy and therapeutic bridge in carefully selected patients undergoing multimodal treatment.