The Value of Somatostatin Receptor Imaging with In-111 Octreotide and/or Ga-68 DOTATATE in Localizing Ectopic ACTH Producing Tumors

OBJECTIVE: We aimed to evaluate the value of somatostatin receptor imaging (SRI) with In-111 octreotide and Ga-68 DOTATATE in localizing ectopic ACTH producing tumors.
METHODS: Nineteen patients who had In-111 octreotide somatostatin receptor scintigraphy (SRS) and/or Ga-68 DOTATATE PET-CT to localize ectopic ACTH producing tumors in between 2000 and 2012 years were included to our study retrospectively. The results of SRI were compared with clinical onset,radiological findings and surgical data of the patients.
RESULTS: Sixteen In-111 octreotide SRS and five Ga-68 DOTATATE PET-CT had been done in 19 patients. In eight out of 19 patients ectopic ACTH secretion site could be detected. In five patients, SRS showed pathologic uptake. In four of these patients, the operations revealed pulmonary carcinoid tumors and in one patient pancreatic neuroendocrine tumor. In one patient, Ga-68 DOTATATE PET-CT revealed pathologic uptake in lung nodule which came out to be pulmonary carcinoid tumor. In another patient who had resections of metastases of atypical carcinoid tumor prior to scans, new metastatic foci were detected both with SRS and Ga-68 DOTATATE PET-CT imaging. In one patient, although SRS was negative, CT which was taken three years later showed a lung nodule which was pulmonary carcinoid tumor. In 11 patients, ectopic ACTH secretion site could not be detected. In 10 of those patients, scintigraphic and radiological imagings could not show any lesions and in one patient, Ga-68 DOTATATE PET-CT was false positive.
CONCLUSION: SRI has a complementary role with radiological imagings in localizing ectopic ACTH secretion sites. PET-CT imaging with Ga-68 peptide conjugates is a promising new modality for this indication.