Tyrosine kinases work to move cells through checkpoints, hastening the cell cycle (and its repetition). When this is out of control--promoted by having the Philadelphia chromosome, cell signaling would also be uncontrolled. This could lead to cancer if cell replication pathways were affected.
Work Step by Step
Review Ch. 12 and material on the nature of cell signaling, paying attention to the role of tyrosine kinases in regulating processes like cell division. This question points out how a seemingly simple change like moving a piece of DNA can have a large effect on gene expression and on the life of the cell and organism.