We report a case of a 66-year-old man with a history of ET, lacking mutations in Janus kinase 2 (JAK2), Calreticulin (CALR), or myeloproliferative leukemia virus oncogene (MPL), who subsequently developed Philadelphia chromosome (Ph)-positive B-cell ALL (B-ALL), harboring a rare e13a3 fusion transcript. This evidence concerns the gene JAK2 and acute lymphoblastic leukemia.