Should myeloid and lymphoid neoplasms with PCM1‐JAK2 and other rearrangements of JAK2 be recognized as specific entities?

Since the publication of the 2001 and 2008 World Health Organization classifications of tumours of haematopoietic and lymphoid tissues, there has been an increasing move towards classification of haematological neoplasms on the basis of the underlying molecular genetic disorder. In recent decades there have been a significant number of reports of haematological neoplasms with rearrangement of JAK2. Published data on such cases have therefore been analysed to determine if any specific entities could be identified. On the basis of this analysis, it is suggested that lymphoid and myeloid neoplasms associated with t(8;9)(p22;p24); PCM1-JAK2 fusion should be recognized as an entity. Furthermore, lymphoid and myeloid neoplasms associated respectively with t(9;12)(p24;p13); ETV6-JAK2 and with t(9;22)(p24;q11·2); BCR-JAK2 should be documented carefully in order to define their features more clearly and assess whether they can be recognized as entities. Identification of all these conditions is important because of the possibility of response to JAK2 inhibitors.