A radioactive diagnostic agent for PET imaging effectively localized primary tumors or metastases in most adults with ectopic Cushing’s syndrome, leading to changes in clinical management for 64% of patients, according to findings from a retrospective study published in Clinical Endocrinology.
As Endocrine Today previously reported, the FDA approved the first kit for the preparation of gallium Ga-68 dotatate injection (Netspot, Advanced Accelerator Applications USA Inc.), a radioactive diagnostic agent for PET scan imaging, in June 2016. The radioactive probe is designed to help locate tumors in adult and pediatric patients with somatostatin receptor-positive neuroendocrine tumors. Ga-68 dotatate, a positron-emitting analogue of somatostatin, works by binding to the hormone.
In a retrospective review, Richard Auchus, MD, PhD, professor of pharmacology and internal medicine in the division of metabolism, endocrinology and diabetes at the University of Michigan, and colleagues analyzed data from 28 patients with ectopic Cushing’s syndrome who underwent imaging with gallium Ga-68 dotatate for identification of the primary tumor or follow-up between November 2016 and October 2018 (mean age, 50 years; 22 women). All imaging was completed at tertiary referral centers at Mayo Clinic, University of Michigan and The University of Texas MD Anderson Cancer Center. Researchers assessed patient demographics, imaging modalities, histopathological results and treatment data. Diagnosis of Cushing’s syndrome was confirmed by clinical and hormonal evaluation. The clinical impact of gallium Ga-68 dotatate was defined as the detection of primary ectopic Cushing’s syndrome or new metastatic foci, along with changes in clinical management.
Within the cohort, 17 patients underwent imaging with gallium Ga-68 dotatate for identification of the primary tumor and 11 underwent the imaging for follow-up. Researchers found that gallium Ga-68 dotatate identified suspected primary ectopic Cushing’s syndrome in 11 of 17 patients (65%), of which seven tumors were solitary and four were metastatic. Diagnosis was confirmed by pathology in eight of the 11 patients: Five patients had a bronchial neuroendocrine tumor, one patient had a thymic tumor, one had a pancreatic neuroendocrine tumor, and one metastatic neuroendocrine tumor was of unknown primary origin. One patient had a false positive scan, according to researchers.
Among the 11 patients with ectopic Cushing’s syndrome who underwent gallium Ga-68 dotatate imaging to assess disease burden or recurrence, the imaging led to changes in clinical management in seven cases (64%), according to researchers.
“Our study demonstrates the high sensitivity of [gallium Ga-68 dotatate] in the localization of [ectopic Cushing’s syndrome], for both occult primary tumors and metastatic lesions,” the researchers wrote. “Importantly, the use of [gallium Ga-68 dotatate] impacted clinical management in 64% of patients with [ectopic Cushing’s syndrome] overall.”
The researchers noted that the high cost and limited availability of PET/CT imaging might preclude the widespread use of gallium Ga-68 dotatate for imaging in patients with suspected ectopic Cushing’s syndrome, and that experience with the scans remains limited vs. other imaging studies.
“Nevertheless, combing the experience of three large referral centers, our study gathers the largest number of [patients with ectopic Cushing’s syndrome] imaged with [gallium Ga-68 dotatate] to date and provides a benchmark for the utility of this diagnostic modality for this rare but highly morbid condition,” the researchers wrote. – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.