JAK2 and myeloproliferative disorder: Certain driver‐related myeloid‐, stem cell‐ and mast cell neoplasms (including CML and JAK2 V617F+ MPN) must be excluded as primary trigger of HE before a diagnosis of CEL can be established, unless co‐existence of such a neoplasm with CEL is demonstrated with certainty based on detailed histopathological and molecular studies (Table S5).