NOL4 is a novel nuclear marker of small cell carcinoma and other neuroendocrine neoplasms.

Neuroendocrine neoplasms (NENs) such as small cell lung cancer (SCLC) and large cell neuroendocrine carcinoma (LCNEC) have characteristic histologies, but immunohistochemistry using neuroendocrine markers is still desirable to confirm diagnosis. CD56 is the most sensitive marker, but also stains various normal tissues and other tumors. Recently, we reported that nucleolar protein 4 (NOL4) is present in the blood of SCLC patients and found it was stained in the SCLC nuclei. In this study, we compared expressions of NOL4 and CD56, using 64 cases of SCLC, 18 cases of LCNEC, 6 cases of atypical carcinoid tumor, 7 cases of typical carcinoid tumor, 68 cases of lung adenocarcinoma, and 62 cases of lung squamous cell carcinoma. For primary lung NENs, sensitivity, specificity, positive predictive value (PPV) and negative predictive value of NOL4 were 77.5%, 95.8%, 93.2%, and 85.1%, respectively, while those of CD56 were 92.1%, 93.3%, 91.1%, and 94.1%. The specificity and PPV of NOL4 were higher than those of CD56, although the differences were not statistically significant. However, NOL4 retains its nuclear immunoreactivity in areas of crush artifact or necrosis. Furthermore, NOL4 was not expressed in adjacent normal tissues including bronchial cells and pneumocytes. Therefore, a combination of NOL4 staining with other cytoplasmic or membranous neuroendocrine markers might enhance diagnostic utility for SCLC and other NENs.