ALK and anaplastic large cell lymphoma: Among systemic ALCLs, the current 2016 WHO classification distinguishes two entities: anaplastic lymphoma kinase (ALK)-positive (ALK+) ALCL, which is in most cases characterized by the t(2;5)(p23;q35) resulting in the expression of the oncogenic NPM-ALK fusion protein and represents approx. 50–60% of all ALCL cases; and ALK-negative (ALK−) ALCL, which lacks t(2;5) and ALK expression [4].