Localization of Unknown Primary Site with 68Ga-DOTATOC PET/CT in Patients with Metastatic Neuroendocrine Tumor

Abstract

Localization of the site of the unknown primary tumor is critical for surgical treatment of patients presenting with neuroendocrine tumor (NET) with metastases. Methods: Forty patients with metastatic NET and unknown primary site underwent 68Ga-DOTATOC PET/CT in a single-site prospective study. The 68Ga-DOTATOC PET/CT was considered true-positive if the positive primary site was confirmed by histology or follow-up imaging. The scan was considered false-positive if no primary lesion was found corresponding to the 68Ga-DOTATOC-positive site. All negative scans for primary tumor were considered false-negative. A scan was classified unconfirmed if 68Ga-DOTATOC PET/CT suggested a primary, however, no histology was obtained and imaging follow-up was not confirmatory. Results: The true-positive, false-positive, false-negative, and unconfirmed rates for unknown primary tumor were 38%, 7%, 50%, and 5%, respectively. Conclusion:68Ga-DOTATOC PET/CT is an effective modality in the localization of unknown primary in patients with metastatic NET.

Trial registration: ClinicalTrials.gov NCT01619865.

Keywords: 68Ga-DOTATOC; PET/CT; neuroendocrine; neuroendocrine tumor; unknown primary.

© 2017 by the Society of Nuclear Medicine and Molecular Imaging.

Figures

FIGURE 1.

68Ga-DOTATOC PET/CT images of patient with liver metastases on CT. In addition to multiple liver lesions, 68Ga-DOTATOC PET/CT shows focus of increased uptake in right lower quadrant (arrows), consistent with ileal NET. Subcentimeter paracaval node is also visible (dashed arrow). Patient underwent resection of primary ileal NET and radiofrequency ablation of liver metastases.

FIGURE 2.

111In-octreotide coronal and transaxial SPECT/CT images (top) and 68Ga-DOTATOC coronal and transaxial PET/CT images (bottom) of patient with liver metastases presenting with Cushing syndrome and unknown primary. Multiple liver lesions were seen on both scans although many more on 68Ga-DOTATOC PET/CT. Pancreatic body lesion is clearly identified on 68Ga-DOTATOC PET/CT images (arrows) but not visualized on the 111In-octreotide SPECT/CT scan obtained 2 mo before 68Ga-DOTATOC PET/CT scan. Patient underwent distal pancreatectomy, adrenalectomy, and radiofrequency ablation of liver metastases.

FIGURE 3.

False-positive 68Ga-DOTATOC PET/CT in patient with ileal lymphoid hyperplasia. Liver metastases seen on whole-body coronal and transaxial PET/CT images (arrow, right top). Mild focal uptake noted in right lower quadrant (arrow) suspicious for ileal NET. Surgical histopathology of ileal resection showed lymphoid hyperplasia.