CTCs are a promising prognostic marker for patients with NETs and should be assessed in the context of clinical trials with defined tumor subtypes and therapy.

Background: Small intestinal neuroendocrine tumours (SI NETs) represent 30–50% of small bowel neoplasms and often present at an advanced stage. To date, there is relatively limited literature regarding prognostic factors affecting overall survival (OS) in stage IV disease. In addition, the prevalence of mesenteric fibrosis (MF) in SI NETs and its effect on OS have not been sufficiently explored in the literature. Aim: The primary aim of this study was to perform a large-scale survival analysis in an institutional cohort of 387 patients with metastatic (stage IV) SI NETs. The secondary aim was to provide epidemiological information regarding the prevalence of MF and to evaluate its effect on OS. Results: The median OS was 101 months (95% CI 84, 118). Age > 65 years, mesenteric metastases with and without desmoplasia, liver metastases, carcinoid heart disease (CHD) and bone metastases were associated with a significantly shorter OS, while primary tumour resection was predictive of a longer OS. The benefit of surgical resection was limited to symptomatic patients. MF was present in approximately 50% of patients with mesenteric lymphadenopathy. Elevated urinary 5-HIAA levels correlated strongly with the presence of CHD (p < 0.001) and to a lesser extent (p = 0.02) with MF. MF and CHD did not usually co-exist, suggesting that different mechanisms are likely to be involved in the development of these fibrotic complications. Conclusions: This study has identified specific prognostic factors in a large cohort of 387 patients with advanced SI NETs and has provided useful epidemiological data regarding carcinoid-related fibrotic complications.

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