Background/aims: In gastroenteropancreatic neuroendocrine tumors (GEP-NETs), primary lesions cannot be resected when the patients have highly advanced disease or when the primary sites are undefined. Such GEP-NETs cannot be evaluated with Ki-67 or the mitotic index. The aim of this study was to examine the prognosis of GEP-NETs that were ungraded by WHO G1-3 grading (U-NET group).
Methodology: Between 2000 and 2011, 75 patients with sporadic GEP-NETs were treated at our institution. The prognosis of patients graded as new WHO grading (G-NET group) was compared with that of the U-NET group. Cox proportional hazard regression analyses were performed to estimate the risk factors for overall survival (OS).
Results: Overall 1-, 3- and 5-year survival rates were 90.7%, 79.9% and 74.9%, respectively. The odds ratio (OR) of patients with synchronous liver metastasis and U-NET was 1.73 (p=0.01) and 5.84 (p=0.002), respectively. Multivariate analyses of OS according to baseline characteristics revealed the only independent risk factor to be U-NET (OR, 3.95; p=0.02).
Conclusions: The malignant potential of U-NET may be no less than that of G-NET, while WHO-G3 patients have the worst prognoses in the G-NET group.