1104P - Functional imaging and clinical outcomes in grade 3 neuroendocrine tumors (NETs G3): A single-center retrospective analysis

Background

Grade 3 neuroendocrine tumors (NETs G3) are a novel category within digestive neoplasms, characterized by Ki-67>20% and a well-differentiated morphology. Previous analyses revealed that NETs G3 might be more heterogeneous than presumed. This study explored a possible prognostic role of functional imaging within NETs G3.

Methods

We performed a retrospective analysis of NETs G3 patients treated at our institute between 2015 and 2021. Timing of NET G3 diagnosis, radiotracers distribution and tumor/non-tumor (T-nonT) ratio (that is SUVs_max in tumor lesions vs. mediastinal blood pool) have been analysed and correlated with clinical outcomes.

Results

Among 30 selected patients, 22 had a NET G3 diagnosis at the beginning of the clinical history (upfront-NET G3) while 8 after years of previous G1/2 NET history (late-NET G3). We reported a better median overall survival (mOS) in cases of ≤30% vs. >30% Ki-67 (p=0.049), homogeneous vs. negative/inhomogeneous ⁶⁸Gallium(Ga)-DOTATOC PET/CT (p=0.004) and negative/inhomogeneous vs. homogeneous ¹⁸Fluorodeoxyglucose(FDG)-PET/CT (p=0.08). We reported a trend to a better mOS for patients with ≥75% concordance between ⁶⁸Ga-DOTATOC and FDG-PET/CT. In cases of <75% concordance (discordance), we reported a significantly better mOS for patients with a prevalent ⁶⁸Ga-DOTATOC vs. FDG-PET/CT (p=0.016). In positive ¹⁸FDG-PET/CT, we reported a better mOS for <4 vs. ≥4 T/non-T ratio (p=0.021). Among upfront-NET G3, patients with concordant exams showed a mOS of 14.5 months (mo). Patients with discordant exams showed a mOS of 24 mo, 56.5 mo for those with prevalent receptor expression and 9.5 mo for those with prevalent FDG uptake. For late-NET G3, we analysed the changes in images over time: before vs. after NET G3 diagnosis, 4/6 patients experienced an increased FDG uptake. One of the latter showed a decreasing receptor expression too; he died 1 mo after NET G3 diagnosis. The other 3 showed a mOS of 64 mo but 2 died at study entry. The 3 patients with concordant imaging, showed a mOS of 64 mo too, but they were all still alive.

Conclusions

Our findings suggested that Ki-67 and functional imaging may allow a more accurate NET G3 subclassification. Prospective studies are needed.

Clinical trial identification

Clinical trial: 2546

Editorial acknowledgement

Legal entity responsible for the study

A. Laffi.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.