An anaplastic lymphoma kinase-positive lung cancer microlesion: A case report

Anaplastic lymphoma kinase (ALK)-positive lung cancers are generally diagnosed at an advanced clinical stage. Herein, we report a case of an ALK-positive lung cancer patient who had a microlesion of this tumor type. The patient was a 51-year-old woman without a smoking history. Computed tomography performed during a lung cancer screening program showed a 7×5-mm subpleural nodule with an irregular border in the right lower lobe. The background lung parenchyma was almost normal. Serum tumor marker levels were not elevated. Histological assessment showed destructive growth in the center of the lesion, as confirmed using Victoria blue-hematoxylin and eosin staining and immunostaining for CD34 and D2-40; however, at the other site, the tumor mainly showed intra-alveolar growth with minor lepidic growth. The tumor cells were positive for thyroid transcription factor-1 and ALK. Fluorescent in situ hybridization of the tumor revealed an ALK gene spilt. Accordingly, the tumor was diagnosed as ALK-positive lung cancer. ALK-positive lung cancer presents diverse histological architectures in the early phase.