Objective: To evaluate the role of ⁶⁸Ga-DOTANOC (⁶⁸Gallium-labeled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-NaI³-octreotide) PET/CT for localization of the primary tumor in patients with carcinoma of unknown primary of neuroendocrine origin.
Material and methods: Twenty patients (median age, 55 years; male 10) with histopathologically proven metastatic neuroendocrine tumor and no localization of primary tumor on conventional imaging were included in the study. PET/CT was done after injection of 132-222 MBq (4-6 mCi) of ⁶⁸Ga-DOTANOC. Images were evaluated by 2 experienced nuclear medicine physicians both qualitatively as well as quantitatively (maximum standardized uptake value). Histopathology (when available) and/or follow-up imaging with biochemical markers were taken as reference standard.
Results: ⁶⁸Ga-DOTANOC PET/CT localized the primary tumor in 12/20 (60%) patients. Midgut was the most common site of primary tumor (n = 9); duodenum (4), ileum (4), and colon (1). In 1 patient each the primary was localized to the pancreas, stomach, and lung. In these 12 patients, significant correlation was found between maximum standardized uptake value of primary tumor and metastasis (ρ = 0.615; P = 0.041). Even in patients in whom no primary tumor was localized, additional sites of metastatic disease were observed when compared with conventional imaging, mostly in lymph nodes and bones. There was a change in management in 3/20 patients (15%), who underwent surgery. In the remaining 17 patients, demonstration of somatostatin receptor expression by PET/CT made them suitable candidate for peptide receptor radionuclide therapy.
Conclusion: ⁶⁸Ga-DOTANOC PET/CT seems to be a promising modality for detecting primary tumor in patients with carcinoma of unknown primary of neuroendocrine origin.