Visualization of tumor heterogeneity in neuroendocrine tumors by positron emission tomography

Excerpt

A 50-year-old woman was diagnosed 15 months ago with a well-differentiated neuroendocrine tumor (NET) of the pancreatic tail (Ki-67: 10 %) and synchronous liver metastases. Consecutively, systemic treatment with octreotide was initiated. Due to progression, 2nd line treatment with peptide receptor radionuclide therapy (PRRT) using the ¹⁷⁷Lu-labeled somatostatin analog DOTA-D-Phe1-Tyr3-octreotide (DOTATOC) was initiated. After three cycles of PRRT, somatostatin receptor (SSTR)-based positron emission tomography (PET) with ⁶⁸Ga-labeled DOTATOC in combination with contrast-enhanced computed tomography (CE-CT) was performed for restaging. In comparison to pre-therapeutic imaging, DOTATOC-PET demonstrated no significant change of both primary and known liver metastases highly expressing SSTR subtype II (Fig. 1, left). However, CE-CT revealed numerous significantly progressive, SSTR-negative intrahepatic lesions, highly suspicious for undifferentiated metastases. Accordingly, a PET/CT with the glucose analog [¹⁸F]fluordeoxyglucose (FDG) was performed. FDG-PET depicted increased focal uptake in all SSTR-negative lesions corroborating the CT findings (Fig. 1, right). Interestingly, almost all SSTR-positive lesions showed no or only weak FDG-accumulation (Fig. 1).

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