Slanted Science

A large collaborative effort has sequenced the entire genomes of two of the most common cancer types: skin (‘melanoma‘) and lung (‘small-cell lung cancer)’. The scientists involved report tens of thousands of mutations in the tumors’ genomes, and speculate that their work may expedite the development of specific drugs to treat these diseases.

Hoorah!

The work is reported in two papers published today in the top-tier science journal Nature. The research was carried out by boffins from many institutes, so suffice it to say that the two lead authors are affiliated with Cambridge University, The Wellcome Trust Sanger Institute, and the Institute Of Cancer Research (all in the UK).

A quick bit of science background: all of the cells in our body have their own set of DNA, which is constantly telling its cell whether it should divide or not. Each set of DNA, throughout our lives, gets mutated by some chemicals and types of radiation (including cigarette smoke and UV radiation from excessive sunlight). It can absorb a certain amount of mutations, but there comes a point where the DNA loses control over the cell it is in charge of. This cell, free of any restrictions, starts on a wild and reckless spree of dividing. It is unable to stop creating more and more copies of itself, forming a constantly growing tumor. This is what is eventually detected by doctors.

But here’s the rub: cells in different parts of our bodies are susceptible to mutations in different parts of their DNA. A mutation which can send a liver cell into uncontrolled replication may have no effect on a kidney cell. So lots of scientists around the world have, in the last few years, been trying to decode the entire DNA sequence from specific types of cancer. Their hope is that they will discover certain mutations which are consistent within a cancer type, and which will thus provide targets for drugs.

That is the significance of this research: we have been given the entire DNA sequence from a skin tumor and a lung tumor.

The scientists report 33,000 and 23,000 DNA mutations specific to each of those respective cancer types. As you’ll remember from earlier, the vast majority of these mutations have no effect on the cell. A few of them, however, will cause the cell to proliferate endlessly.

Each of these current studies looked at just a single patient’s DNA, meaning that while the results are important – and may have identified certain regions of DNA (‘genes‘) which contribute to the cancers – there is a lot of work ahead to progress this to somewhere clinically useful.

For example – and this will be best understood by professional biologists – these studies both used cell lines as the source of their DNA. That is, they did not look at the DNA sequences of tumors directly as they were removed from the patient. Rather, they grew them in the lab for some time before examining the DNA. It is well understood that doing this can introduce even more mutations into the cells’ DNA, as well as enhancing the growth of sub-populations of cells which may slant the results.

All in all, a significant pair of papers, which in our opinion are of limited use other than as an indicator of the gigantic leaps which the many similar studies currently in progress will soon deliver.

Don’t Hold Your Breath, But This May Lead To: disease-specific drugs. Currently, doctors use a few, broadly-acting drugs to treat many types of cancer. If we can identify the specific mutations which drive growth of – for example – a bone cancer versus a bowel cancer, then we can begin to design drugs specific for each. As well as improved efficacy in treating the cancer, this will also mean that patients will suffer fewer of the nasty side effects they currently experience (hair loss, nausea, immune-suppression, etc).