8. Clonal Selection

The chances of any individual cell randomly gaining the combination of mutations needed to make it malignant is very small, infact nearly impossible. So why are cancers so common, and how do they gain these mutations?

On prominent theory is clonal selection. Tumours are clones - that is they are all the offspring of a single mutated cell. But they also mutate quickly and as a result they are genetically diverse.

Some cells gain mutations which make them better at competing for space and resources. These cells will outcompete their neighbours. These cells will form a tumour with the new mutation. This sequence repeats over and over until the cell has enough of the mutations to make it cancerous.

One well described example of this is colon cancer. Colon cancers often develop from benign tumours - adenomas. As cells within the adenomas gain more mutations, they form new clones with an enhanced ability to grow. When they gain the ability to invade the surrounding tissue, they become cancerous.