What are the key characteristics of cancer cells and how do they arise?

Cancer cells are continually dividing in an uncontrolled manner and have adapted mechanisms of avoiding cell death. They are also more mobile and are capable of spreading to different parts of the body to form secondary tumours in a process called metastasis. They arise through mutations in 2 types of genes: tumour suppressor genes and proto-oncogenes. These genes have important roles at checkpoints in the cell cycle and control the speed at which cells grow and divide. Tumour suppressors usually act like breaks on the cell cycle. They prevent cells from progressing through the stages of the cycle. This means that the cells grow slower and divide less. Mutations in both copies of a tumour suppressor gene will mean that these breaks are lost, allowing the cell to grow faster and divide more often. Proto-oncogenes usually promote the cell cycle (they act as accelerators) but are only activated when the cell needs to divide. Mutations in proto-oncogenes can make them permanently active. Now called oncogenes, they constantly promote the cell cycle and therefore the cell grows faster and divides very frequently. It takes mutations to multiple tumour suppressor genes and proto-oncogenes to transform healthy cells into cancer cells.