Assuming that NPM-ALK proteins rely on the formation of the heterodimers to migrate into the nuclei/nucleoli of ALK+ALCL cells, the relative paucity of the heterodimers in the RU cells suggests that NPM-ALK proteins dissociate from FL-NPM1 after their entry into the nucleus and possibly complex with other proteins. This evidence concerns the gene NPM1 and anaplastic large cell lymphoma.