Tumor Cystic Necrosis Following Peptide Receptor Radionuclide Therapy in Neuroendocrine Tumors.

The response assessment to peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumors is complex. We present the case of a 49-year-old man with metastatic rectal neuroendocrine tumor whose clinical symptoms and response evaluation criteria in solid tumors suggested progressive disease following PRRT. However, Ga-DOTA-(Tyr3)-octreotate PET/CT showed a partial scintigraphic response with absence of F-FDG PET/CT uptake consistent with tumor cystic necrosis. Long-term follow-up confirmed ongoing tumor response to treatment. Utilizing all modalities of response assessment seems to be important in correctly judging the benefit from PRRT and will need to be incorporated when developing response assessment tools.