ALK (Anaplastic Lymphoma Kinase, cd246) is a transmembrane receptor of leucine kinase with molecular weight about 200 kDa. ALK gene was found in CD30 + anaplastic large cell lymphoma cases in 1980. If there is genetic translocation, tumor cells will produce a kind of NPM-ALK heterozygous protein (also known as p80). In normal tissues, a few cells express ALK, such as glial cells, neurons and so on. In tumor cases, literature has shown that ALK is expressed in anaplastic large cell lymphoma, inflammatory myofibroblastic tumor, rhabdomyosarcoma, leiomyoma and lung adenocarcinoma.