Histomorphologic features of lung adenocarcinomas exhibiting ALK gene rearrangement.

With the advent of tyrosine kinase inhibitors, the identification of tumors with alterations in tyrosine kinase genes has become important to guide treatment. Lung adenocarcinomas harboring ALK translocations may be targeted with drugs such as crizotinib. We undertook a retrospective review of our institution's pathology records from January 2015 through September 2017 and identified 10 lung adenocarcinomas with ALK rearrangements. We reviewed the histomorphologic features and immunohistochemical results from these 10 cases. Morphologic features included patterns such as acinar, papillary, micropapillary, and solid, as well as features such as cribriform, signet ring, and extracellular mucin. Acinar (including simple and cribriform) was the most common pattern, followed by papillary. Solid and signet ring features were the least common. These findings were consistent with prior histomorphologic studies of ALK-positive lung adenocarcinomas. Certain histomorphologic patterns are associated with ALK positivity. However, histomorphologic features are neither absolutely sensitive nor absolutely specific in suggesting ALK rearrangement. Thus, identification of lung adenocarcinomas that may benefit from treatment with tyrosine kinase inhibitors requires comprehensive molecular testing.