Clinicopathological Characteristics of Low to Intermediate Grade Neuroendocrine Tumors with Oncocytic Features

Neuroendocrine tumors (NETs) with oncocytic features are rare. To date, few studies have described the metastatic characteristics of these tumors, most of which were limited by the low number of cases. One article characterized intermediate to high grade (G2 and G3) oncocytic NETs of the pancreas as having an ominous outcome; however, metastatic features of low-grade oncocytic NETs have, to our knowledge, been hitherto unexplored. Our study characterized the clinicopathological and metastatic features of 32 low to intermediate-grade oncocytic NETs of various organs. The most frequent metastatic site was the liver (63%). The metastatic rate of our cases was compared with Riihimaki’s study (metastatic rate of G1/G2 NETs was reported), as well as Heetfeld’s study and Lithgow’s study (metastatic rate of G3 NETs was reported). The overall metastatic rate of our cases is 84.4%, which is significantly higher than that of the G1/2 NETs from Riihimaki’s study (84.4% vs. 25%, p < 0.0001), while similar to that of the G3 NETs from Heetfeld’s study (84.4% vs. 86.5%, p > 0.05) and Lithgow’s study (84.4% vs. 80.8%, p > 0.05). These data indicate that oncocytic features could potentially be characterized as high-risk features in addition to high Ki-67 index, mitotic count, and necrosis. Thus, imaging studies such as liver magnetic resonance imaging (MRI) may be warranted to detect liver metastases in NETs with distinctive oncocytic cytologic features even in the absence of other high-risk features.