JAK2 and cancer: An increasing amount of evidence has demonstrated that PBXs play crucial roles in cancer progression by modulating cancer‐related signalling pathways, such as the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3), mitogen‐activated protein kinase (MAPK), and the phosphatidylinositol 3‐kinase (PI3K)/AKT, signalling pathways.