ALK and non-Hodgkin lymphoma: Anaplastic large cell lymphoma (ALCL) was introduced as a unique variety of non-Hodgkin lymphoma in the 2001 version of the World Health Organization (WHO) classification [8]; ALK+ ALCL was later listed in the 2008 version of the WHO classification [9]; and, ALK-negative ALCL was recently added in the 2016 version of the WHO classification [10].