Anaplastic lymphoma kinase (ALK) belongs to the insulin receptor superfamily. It is a transmembrane receptor protein tyrosine kinase that can form a fusion protein with the nuclear protein gene nucleophosmin (NPM). ALK can be active in cancer through various mechanisms. Protein expression by tumor cells is an independent prognostic factor that predicts a favorable outcome. ALK staining is positive in about 60 % of anaplastic large cell lymphomas (ALCL). Abnormal expression of the protein has also been detected in various solid tumors, such as non-small cell lung cancer (NSCLC) and brain tumors.