First Autopsy-confirmed Complete Remission of Metastatic Neuroendocrine Neoplasm of Tailgut Cyst After a Single Cycle of Alpha–Peptide Receptor Radionuclide Therapy With [225Ac]Ac-DOTA-LM3

A 78-year-old man with neuroendocrine neoplasm (NEN) G2 originating from a presacral tailgut cyst was previously treated with surgery, lanreotide and [177Lu]Lu-DOTATATE peptide receptor radionuclide therapy (PRRT). Due to recurrence, confirmed by [68Ga]Ga-DOTA-LM3 PET/CT, which showed local, hepatic, lymph nodal, soft tissue, and cardiac disease, he received 1 cycle of PRRT with somatostatin receptor (SSTR)-antagonist DOTA-LM3 labeled with alpha-emitting Actinium-225. Due to rising levels of bilirubin 2 months after therapy, an endoscopic retrograde cholangiopancreatography diagnosed bile duct stenosis and gastric adenocarcinoma (cause of death). Autopsy findings did not reveal any residual NEN, indicating complete remission after one cycle of alpha-PRRT.