ALK and anaplastic large cell lymphoma: The World Health Organization’s 2016 classification system categorizes ALCL into four types on the basis of ALK expression: systemic ALK-positive ALCL (ALCL, ALK+), systemic ALK-negative ALCL (ALCL, ALK−), primary cutaneous ALCL (pcALCL), and breast implant-associated ALCL (BI-ALCL) [11–13].