450P - Are grade III well-differentiated neuroendocrine tumours a unique clinic-pathological entity?

Background

Neuroendocrine neoplasms (NENs) are a rare group of malignancies with significant mortality. Recently, Grade 3 (G3) NENs have been dichotomised into well-differentiated neuroendocrine tumours (NETs) and poorly differentiated carcinomas (NECs), with seemingly different characteristics. Treatment for these groups differs, although there is not enough evidence to identify a uniform standard of care. We aim to understand whether the difference between NET and NEC G3 is clinically significant, and if so, what these are in terms of their clinical characteristics.

Methods

A retrospective cohort study was done to identify patients diagnosed with NEN G3 in Nottinghamshire. Patients were included if they were diagnosed after 2017 with Ki-67 score of >20%, which is metastatic and not amenable to curative treatment. Patients with neoplasms that exhibit large- or small-cell like morphology were excluded. Clinical characteristics and treatment were collected and analysed using Kaplan-Meier curves and ANOVA.

Results

22 patients were included. The mean overall survival (OS) of the cohort was 778 days and the median OS was 461 days. Median OS for patients with Ki-67 score ≥40% was 861 days, as compared to 217 days for patients with a score <40% (p=0.078). Median OS for patients with unknown primary site was worse, followed by pancreatic (217 days vs 461 days; p=0.939). Mean first-line progression free survival (PFS) for patients who did not receive platinum-based chemotherapy was numerically superior than for patients who did receive this (449 vs 127 days; p<0.001). Mean first-line PFS for patients who received alkylating-based chemotherapy was higher than for patients who did not receive this (228.22 vs 156.46 days; p=0.003). Capecitabine and temozolomide treatment had the best objective response rate at 54.5%.

Conclusions

This study described the histopathological and clinical factors of high-grade NENs. These findings contribute to a better understanding of the prognostic significance of factors in this group of neoplasms, sufficient to rationalise a difference in care for patients with G3 NETs and true high-grade NECs.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.