We then used it to determine NPM-ALK fusion protein expression levels in ALCL cell lines and to confirm the NPM-ALK/ β-actin ratios determined by ELISA using those independently determined by two-dimensional electrophoresis and we estimated that NPM-ALK fusion protein is expressed at substantial levels in human ALCL as compared to the ubiquitous β-actin protein. Here, ALK is linked to anaplastic large cell lymphoma.