The recent publication of two “Cancer Genomes” in Nature has caused some buzz concerning the actual relevance of these findings. Let’s take a look at what was actually studied, and why it’s so exciting.

Each person has their own genome, that is, ALL of our DNA, which is unique to each person. So what is a cancer Genome? In reporting the two articles, Nature provides a succinct description:

Tumours develop when a normal cell’s DNA is damaged, allowing that cell to proliferate unchecked.

So a tumor is characterized by rapid, abnormal and unchecked growth, but it also has mutations that are associated with that growth. These are somatic mutations: they occur in our bodies as opposed to our eggs and sperms. Somatic mutations are not inherited, they occur all over our bodies, but rarely lead to cancer. In tumors, there are MANY somatic mutations. In these papers, they described 33,345 mutations for melanoma and 22,910 mutations for lung cancer. The question is which mutations caused these cells to grow so rapidly?

The question is further complicated because the large number of mutations may have occurred after the cell became cancerous. That is, DNA repair mechanisms were damaged and so all those mutations were allowed to accumulate. How can we tell the difference between the mutations which cause cancer, and the mutations which are the effect of cancer? All these questions make studying the genetics of cancer so difficult.

So what do these papers contribute to our understanding of cancer genetics? For starters, it appears that most of the mutations are likely caused by the chemical agents which are known causes of these types of cancers: Tobacco smoke and ultraviolet light. That highlights the preventable nature of these cancers, which kill some 250, 000 people annually. An exciting finding is that there seems to be more mutations in non-coding regions of the genome than coding. Remember that coding regions are parts of the genome where protein-coding genes are located. Mutations in genes are much more likely to have a deadly effect than in non-coding regions because they are likely to have a functional consequence.

These findings are not immediately applicable to people’s everyday lives, in terms of developing therapeutic treatment, but most fundamental research isn’t. The point here is that the first steps to understanding the genome of a tumor as a whole are being taken, which broadens our understanding of cancer one step at a time.

Here are the abstracts of the two articles:
A comprehensive catalogue of somatic mutations from a human cancer genome
Pleasance, E. D. et al. Nature advance online publication doi:10.1038/nature08658 (2009).

A small-cell lung cancer genome with complex signatures of tobacco exposure
Pleasance, E. D. et al. Nature advance online publication doi:10.1038/nature08629 (2009).