Endocrine Abstracts (2019) 68 P1 | DOI: 10.1530/endoabs.68.P1

Size still matters for appendiceal neuroendocrine tumours (aNETs)

Edward Alabraba1, Hassan Malik2, Melissa Banks2, Mark Pritchard3, Daniel Cuthbertson2, Graeme Poston2 & Stephen Fenwick2

1Queens Medical Centre, Nottingham, UK; 2University Hospital Aintree, Liverpool, UK; 3Royal Liverpool Hospital, Liverpool, UK

Background: Appendiceal neuroendocrine tumours (aNETs) are usually diagnosed incidentally at appendicectomy, are indolent and rarely recur.

Methods: We retrospectively analysed patients diagnosed with aNETs and entered prospectively into our tertiary referring centre’s NET database between 1990 and 2016.

Results: 102 patients (F:M ratio of 1.04:1) presented with aNET at a median age of 39.4 (range 16.3–81.1) years. Average tumour size was 12.7 (range 1–60) mm. The most reliable IHC markers for aNET diagnosis were CD56, CgA, and SYP. The appendiceal tip was the site of 63% of aNETs. Appendicectomy was the most common diagnostic index operation in 79% of cases, followed by 21% who underwent colectomy. 30 patients had completion surgery at a median of 3.2 (range 1.4–9.8) months after index surgery. Univariate logistic regression identified male gender (P=0.002), young age at diagnosis (P=0.002), ENET stage ≥2a (P≤0.034), size ≥ 2 cm (P=0.001), R1 (P=0.001), PNI (P=0.013), and involvement of appendiceal base (P=0.008) as significantly associated with selection for completion surgery. Histology from completion surgery showed residual NET disease in 9 patients comprising lymph nodes alone (n=8) and residual tumour in caecum (n=1). Univariate logistic regression showed likelihood of residual disease was significantly predictedby tumour size ≥2 cm (P=0.020). Residual disease did not affect relapse or death. Relapse occurred in 2 patients at a mean of 17.6 (range 16.5–18.8) years. Univariate logistic regression showed risk of relapse was significantly predicted by PNI (P=0.034) but tumour size ≥2 cm was not significant (P=0.089). There were 5 deaths in our series, of which 1 was NET-related. The 5-year and 10-year overall survival of NET patients were 98% and 92%; both unaffected by ENET stage or resection margin status (P≥0.637). The 5-year and 10-year progression free survival of aNET patients were 96% and 92%. Only 5-year PFS was significantly affected by ENET Stage (P=0.002).

Conclusion: aNETs have a long latency period before recurrence mandating extended follow-up in patients with PNI and possibly tumour size ≥2 cm. Tumour size >2.0 cm predicts residual disease at completion surgery. ENET stage significantly affected 5-year PFS but overall survival was unaffected.

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