According to the information provided in the question, a healthy cell from a chicken's stomach completes a full cell cycle in 625 minutes whereas a cell that has cancer only requires 450 minutes. This shows that cancerous cells would be able to reproduce at a rate that is faster than the rate at which normal cells can reproduce. The result is the cancer spreading and affecting a larger portion of the chicken's stomach.
All cells die after a certain duration of time. A balance is achieved due to the new cells that are created to replace those that die. If the rate of creation of new cells is faster than the rate at which they die, the number of cells grows in number exponentially.