Motivated by the facts that expression of full-length ALK is absent in hematopoietic cells, and that NPM-ALK fusion protein is a specific biomarker of ALCL with a long half-life of 48 hours38 we developed an immunoassay for NPM–ALK fusion protein by using human ALK+ ALCL cell lines after screening various antibodies that recognize both the ALK and the fusion portion of the NPM-ALK fusion protein. The gene discussed is ALK; the disease is anaplastic large cell lymphoma.