Neuroendocrine tumor (NET) occurring in association with other endocrine syndromes forms a distinct entity. The aim was to assess the therapy response profile of the routine peptide receptor radionuclide therapy (PRRT) in this relatively uncommon but clinically challenging subgroup of patients. A retrospective analysis was undertaken from the case records from those who were treated with ¹⁷⁷Lu-DOTATATE for metastatic NET. In addition to assessing the therapeutic efficacy, emphasis was also given to study lesional sites and scan pattern. A total of 5 cases were found: In this series of five cases, four belonged to multiple endocrine neoplasia type 1 (MEN1) syndrome; in these four MEN1 syndrome patients, the primary site of NET was thymic region (n = 1), duodenum (n = 1), and pancreas (n = 2). The fifth case was of Cushing's syndrome with the primary site of NET in the thymus. A good symptomatic response was observed in all MEN1 syndrome cases (100%) and progression of symptoms in the patient with Cushing's syndrome. The biochemical response (assessed by measurement of tumor marker serum chromogranin A) demonstrated very good partial response (defined by more than 75% reduction of tumor marker) in 2 MEN1 cases and Cushing's syndrome, good partial response (25-75% reduction of tumor marker) in the remaining 2 MEN1 cases. Scan wise (assessed by technetium [^99mTc]-hydrazinonicotinamide [HYNIC]-tektrotyd [TOC]/⁶⁸Ga-DOTA-NOC/TATE positron emission tomography-computed tomography [PET-CT] and fluorodeoxyglucose [FDG] PET-CT) partial response was observed in 3 MEN1 cases, stable disease was noted in one MEN1 case and disease progression was noted in the patient with Cushing's syndrome. The change in FDG uptake was found to be an important sensitive scan parameter in the treatment evaluation of NETs compared to somatostatin receptor-based imaging in the cases with low MiB1 index. In our series, good palliative response to ¹⁷⁷Lu-DOTA-octreotate (DOTATATE) PRRT was observed in most NET patients associated with MEN1 syndrome without any major hematological or renal toxicity.

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