Clinical features and outcomes of appendiceal neuroendocrine tumours: 10 year audit from the Irish NET Centre of Excellence

Appendiceal neuroendocrine tumours (aNETs) are rare neoplasms of the gastrointestinal tract often diagnosed incidentally at the time of appendicectomy. Appendicectomy is considered curative in the majority of cases but guidelines recommend right-sided hemicolectomy (RHC) for those with specific high-risk features despite no data supporting a survival benefit. We performed a retrospective search of multi-disciplinary tumour board and pathology databases from 2012 to 2022 to identify cases of aNET treated at our centre. Follow-up data were obtained from the electronic healthcare records. A total of 142 cases of aNET were included for analysis. Mean age at presentation was 34, of which 76% were female and 92% of aNETs were located in the tip/middle of the appendix; 90% were grade 1, and 93% had R0 resection. Tumour size was 2 cm in 9%. A total of 43 patients (30%) underwent RHC with lymph node metastases identified in 16 (37%). Lymph node metastases were associated with tumour size >2 cm (p = .008) and higher tumour grade (p = .041) on multivariate analysis. For aNET 1-2 cm, lymph node metastases were identified in 7/22 who had RHC (32%) with tumour grade the only significant risk factor (p = .046). Distant metastases were identified in 2 cases (1%), diagnosed synchronously and associated with grade 2 tumours. Overall survival for those with lymph node metastases was 100% after a median 4 years. Progression-free survival was 93%, with a single case of disease progression associated with synchronous distant metastases at initial diagnosis. Lymph node metastases in aNET are associated with higher tumour grade and tumour size >2 cm. Disease progression in the setting of lymph node metastases is rare. The significance of lymph node metastases and need for completion RHC remains uncertain.