An Unusual Observation in Metastatic Neuroendocrine Neoplasm: Diffuse Pattern Hepatic [⁶⁸Ga]Ga-DOTATATE Uptake Related to Micro-metastatic Disease and Discordance between Dual-Tracer PET-CT Findings and MIB-1 Labelling Index

Abstract

Neuroendocrine neoplasms (NENs) are a rare and diverse group of neoplasms that can originate from neuroendocrine cells in any organ. We herein present a patient with Grade II neuroendocrine tumor (NET) of the pancreas with bilobar liver metastasis and a MIB-1 labelling index of 15%, who underwent various systemic and targeted therapies. On follow-up, dual-tracer PET-CT imaging with [⁶⁸Ga]Ga-DOTATATE PET/CT showed new onset skeletal metastases and diffuse pattern SSTR (somatostatin receptor) expression in the left lobe of the liver (Krenning score 3), contrasted by absent uptake on [¹⁸F]FDG. Magnetic resonance imaging of the liver confirmed sub-centimetric left liver lobe lesions, further biopsy of which suggested Grade-III NET exhibiting high Ki-67 (55–60%). Thus, a discordance was observed between Ki-67 and the dual-tracer PET-CT findings, emphasizing the complexity of NEN imaging (with possibility of differentiation even in a relatively high Ki-67) and the importance of using multiple tracers for accurate assessment in guiding evidence-based management strategy.

Keywords

metastasis - NET - DOTATATE - FDG - PET - discordance - de-differentiation - dual-tracer PET

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