Lymph node metastases are more frequent in paediatric appendiceal NET ≥1.5 cm but without impact on outcome - Data from the German MET studies.

ABSTRACT

BACKGROUND: Paediatric appendiceal neuroendocrine tumours (appNET) are very rare tumours, mostly detected incidentally by histopathological evaluation after appendectomy. Treatment recommendations are based on adult data considering high-risk NET as defined by European Neuroendocrine Tumour Society (ENETS) guidelines for completion right-sided hemicolectomy (RHC). Recent data suggest that less aggressive therapy may be justified. PROCEDURE Analysis of children and adolescents with appNET prospectively registered with the German Malignant Endocrine Tumour (MET) studies between 1997 and 2022. RESULTS: By December 2022, 662 patients (64.7% females, 35.3% male) had been reported. Median age was 13.3 years [4.5-17.9], median duration of follow-up 2.2 years [0-10.9]. No distant metastases were reported. Tumour size was <1 cm in 63.5%, 1-2 cm in 33.2%, and >2 cm in 3.2% of patients. WHO grade 1 and 2 tumours were diagnosed in 76.9% and 23.1% of patients, respectively. Lymphovascular invasion and lymph node metastases were associated with tumour size ≥1.5 cm. 27.0% of patients presented with high-risk NET according to ENETS criteria. Of those, only 55.9% underwent secondary oncological right hemicolectomy. Neither distant metastases, nor recurrences or disease-related deaths occurred in patients with appendectomy only as well as in patients with completion RHC. Overall and event-free survival were both 100%. CONCLUSIONS: Internationally harmonized consensus recommendations on treatment of children and adolescents with appendiceal NET are urgently needed to avoid completion RHC in high-risk patients.