Histologic Features of ALK-Expressing Adenocarciomas of the Lung

ABSTRACT

PURPOSE: This study was designed to define the specific histologic features of anaplastic lymphoma kinase (ALK)-expressing pulmonary adenocarcinoma. MATERIALS AND METHODS: Of the 580 pulmonary adenocarcinomas diagnosed between March 2010 and February 2011, immunohistochemical staining for ALK was performed in 269 cases showing any suspicious histologic features in previous reports. The subtype according to the World Health Organization classification and the characteristic histologic features were re-evaluated in ALK-expressing cases. RESULTS: A total of 46 cases (7.9% of the 580 adenocarcinomas, 17.1% of the 269 studied cases) were positive for ALK. Among the 46 cases showing ALK positivity, 35 cases (76%) showed intra- and/or extra-cytoplasmic mucin. The most well-known characteristic finding associated with ALK, signet ring cells, was found in 18 cases (39.1%). Cribriform pattern with extracytoplasmic mucin was identified in five cases. In six cases, all three features were found. On the other hand, there were three other cases that did not show any of the aforementioned histologic features. In 12 lobectomy specimens, the most common histologic pattern was a solid pattern (five cases, 41.6%). CONCLUSION: Intra- and/or extra-cytoplasmic mucin, including signet ring cell appearance and a cribriform pattern with extracytoplasmic mucin, are characteristic features of ALK-expressing non-small cell lung cancer.