Oncocytic neuroendocrine tumors of the lung: Histopathologic spectrum and immunohistochemical analysis of 15 cases

Oncocytic neuroendocrine tumor of the lung is rare. To reveal the clinicopathologic features of oncocytic neuroendocrine tumor, we reviewed surgical resections from 80 patients diagnosed with carcinoid tumors and 35 high-grade neuroendocrine carcinomas. We discovered 7 cases from the 80 carcinoid tumors and added 8 patients from personal consultation files. There were no statistically significant differences among the clinical features (such as age, location, and survival). Although most oncocytic neuroendocrine tumors were low-grade neuroendocrine carcinomas, we found that they could be of any grade. Tumor cells showed an ample amount of granular oncocytic cytoplasm and had a round-to-oval nucleus with coarse chromatin. Two cases mainly consisted of small-sized to medium-sized cells resembling plasma cells. This tumorous area intermingled with the conventional oncocytic area. Other histologic features were a large conspicuous nucleolus in 9 cases and the presence of giant cells in 8 cases. In the 80 carcinoid cases, bone formation (P = .034), the presence of giant cells (P=.021), and tumor cells with a conspicuous nucleolus (P = .021) were more frequently observed. Immunohistochemical analysis revealed that oncocytic cells were positive for antimitochondria antibody. In conclusion, most of the tumors were low-grade neuroendocrine carcinomas, but we found that oncocytic neuroendocrine tumor can display features of high-grade neuroendocrine carcinoma. The oncocytic change was induced by accumulation of mitochondria. Although this variant does not differ in clinical features of nononcocytic neuroendocrine tumors, histologic features of the oncocytic neuroendocrine tumor can be a potential cause of diagnostic error.