Anaplastic lymphoma kinase (ALK) is a receptor protein-tyrosine kinase. In anaplastic large-cell lymphomas,translocation between the NPM gene and the ALK catalyticdomain produces a constitutively active fusion protein thatdrives tumorigenesis. ALK immunostaining is a valuablemarker in identifying anaplastic large-cell lymphoma (ALCL)and other ALK-positive malignancies. Detection of ALKprotein contributes to the research characterization oflymphoid neoplasms and is commonly used in translationaland exploratory oncology studies.