Endocrine Abstracts

Background: Accurate imaging is essential for NETs. 111In-octreotide scintigraphy, 68Ga-DOTATOC PET/CT and 18F-FDG PET/CT are the most commonly used modalities. This study compared the three modalities to ascertain the added value of newer functional imaging approaches.

Methods: A retrospective review was performed on patients who underwent 68Ga-DOTATOC PET/CT and 18F-FDG PET/CT between 07/2018 and 03/2023 as part of a clinical trial at BC Cancer. Patients with 111In-octreotide scintigraphy within one-year prior to their DOTATOC and FDG scans were included if all three scans included the number of detected lesions. Descriptive statistics were used to evaluate the three modalities.

Results: Of the 102 patients identified, 45.1% were female and median age at diagnosis was 61 years (IQR 51-69). The most common primary sites were small intestine (44.1%), pancreas (17.6%), unknown (12.7%), lung and stomach (both 9.8%). Median time between octreotide and DOTATOC scans was 120 days (IQR 66-203) and 4 days (1-11) between DOTATOC and FDG scans. DOTATOC had the highest positive scan rate of 73.5% (75/102, 95% CI [63.9, 81.8]) and a mean number of detected lesions of 5.75 (p < 0.001) compared to octreotide (53/102, 52.0%, 95% CI [41.8, 62.0]) with a mean of 1.98 lesions and FDG (34/102, 33.3%, 95% CI [24.3, 43.4]) with a mean of 2.00 lesions. The most common imaging profiles were Octreotide+DOTATOC+FDG- (28/102, 27.5%), Octreotide-DOTATOC-FDG- (20/102, 19.6%), Octreotide+DOTATOC+FDG+ (19/102, 18.6%) and Octreotide-DOTATOC+FDG- (16/102, 15.7%). Among patients with an initial negative octreotide scan (n=49), 59.2% (29/49) showed positive findings on one or both of DOTATOC or FDG (16/49, 32.7% DOTATOC only; 1/49, 2.0% FDG only; 12/49, 24.5% both), with a median DOTATOC Krenning score of 3 (range 1-4). In patients with either a positive octreotide or DOTATOC scan (n=81), lesion count concordance was observed in 13.6% (11/81), with DOTATOC exhibiting a higher lesion count in 87.1% (61/70) of the discordant scans. Among patients with at least one positive scan (n=\82), only 6.1% (5/82) had a higher lesion count on FDG. In patients metastatic at baseline (n=65), DOTATOC and FDG were able to detect liver and bone lesions not observed on octreotide in an additional 17 (13/17, 76.5% DOTATOC only; 2/17, 11.8% FDG only; 2 both) and 9 (7/9, 77.8% DOTATOC only; 2/9, 22.2% both) patients, respectively.

Conclusion: These findings highlight the potential benefit of incorporating 68Ga-DOTATOC PET/CT with/without 18F-FDG PET/CT for improved detection of NETs compared to 111In-octreotide scintigraphy.

Abstract ID 23755