Endocrine Abstracts

Background: PRRT is an effective treatment option (especially for controlling disease progression)for disseminated neuroendocrine tumors (NETs), with good expression of the somatostatin receptors. Despite significant progress in NET personalized management, searching for novel predictive and prognostic factors of response to PRRT is crucial for more effective follow-up, better treatment choices leading to more favorable final outcome. Some recent studies indicate that the response to PRRT assessed on the basis of imaging of somatostatin receptors may be a potentially useful tool for prediction of overall PRRT effect.

Methods: 10 patients with disseminated NET lesions who underwent [68Ga]Ga-DOTA-TATE-PET/CTs before and after PRRT were eligible to the analysis. 5 patients received 177Lu-DOTA-TATE whereas 5 tandem (mix 1:1 of 177Lu- and 90Y-DOTA-TATE)therapy. PET/CTs examinations were performed on average 3.2 months before and 4.6 months after treatment. For all measurable metastatic lesions in both PET/CTs(before and after PRRT) the corrected SUVmax was calculated as the ratio of SUVmax of lesion to SUVmax of normal liver tissue. The next step was to evaluate the change of corrected SUVmax between PET/CTs done before and after PRRT, compared to the first PET/CT. Finally, those results were complied with the result of PRRT assessed after mean follow-up time 20.3 months as: 1. Partial response (PR) 2. Stabilization(SD) 3. Progression(PD) of the disease.

Aim: Assessment if corrected SUVs change in 68Ga-somatostatin analogue PET/CT in response to PRRT may have a predictive value in patients with NET and if it differ in between PRRT with 177Lu-DOTA-TATE alone or tandem therapy.

Results: During follow-up the PR was confirmed in 1 patient, 4 had stabilization and 5 progression of the disease. Among the whole group of lesions there was a mean 27.3% reduction in corrected SUVmax in comparison between PET/CTs done before and after PRRT, and 27.4% and 27.2% reduction in Lu-177 group and tandem group, respectively. The decrease of lesion’s corrected SUVmax for patient with PR was 56.4%for tandem therapy, in none of patients treated with 177Lu-DOTA-TATE regression was observed. In the SD group the average decrease od SUVmax was 42.9%for Lu-177 and 8.7%for a tandem PRRT. In patients with PD the increase in corrected SUVmax was observed, 3.6%for Lu-177 and 14.6%for tandem therapy.

Conclsion: A decrease of the mean value of corrected SUVmax in metastatic NET lesions after PRRT may have a predictive value in estimation of progression risk. There were no statistically significant differences in SUVmax changes between 177Lu-DOTA-TATE and tandem therapy.