Final answer:
Cancer cells form when there is a disruption in the cell cycle due to changes in the DNA sequence of genes that regulate the cell cycle.
Step-by-step explanation:
When a disruption occurs in the cell cycle, it allows for the formation of cancer cells. Cancer is the result of unchecked cell division caused by a breakdown of the mechanisms regulating the cell cycle. This breakdown can occur due to changes in the DNA sequence of genes that code for regulatory molecules, leading to faulty instructions and nonfunctional proteins. As a result, the monitoring system of the cell cycle becomes disrupted, allowing for the passing on of mistakes to daughter cells and the accumulation of damage. This eventually leads to the formation of rapidly reproducing cancer cells that crowd out normal cells and result in tumorous growth.