In a massive undertaking, researchers have scanned the entire genomes of breast cancer cells and mapped the clearest ever picture of which genetic mutations cause the disease to occur. For the two studies, published in Nature and Nature Communications, a team of international scientists developed a “near perfect” image of all the genetic mishaps that cause otherwise healthy tissue to become cancerous.

Previous studies had looked at only the mutations that occur in the regions of the DNA that directly code for proteins. Yet this accounts for only about 1 or 2 percent of the entire human genome, meaning that the vast majority of the cancerous cells' DNA went unexamined. This latest study has now filled it all in, looking at the 3 billion letters of genetic code that make up the non-coding section of DNA from 560 breast cancers.

They found that there were a total of 93 genes that, if mutated, led to the development of breast cancer. Some of these alterations in the DNA were associated with repair mechanisms, as well as the function of the tumor suppressors BRCA1 and BRCA2, which were already known to be implicated in breast cancer. The researchers expect that the comprehensive list of genes is almost certainly definitive, bar a few incredibly rare mutations.

^{Around 50,000 women and 350 men will be diagnosed with breast cancer every year in the U.K. CristinaMuraca/Shutterstock}

“There are about 20,000 genes in the human genome. It turns out, now we have this complete view of breast cancer – there are 93 of those [genes] that if mutated will convert a normal breast cell into a breast cancer cell,” said Sanger Institutes’ Professor Sir Mike Stratton, one of the studies many co-authors, to BBC News. “That is an important piece of information. We hand that list over to the universities, the pharmaceuticals, the biotech companies to start developing new drugs because those mutated genes and their proteins are targets for new therapeutics.”

It is likely, however, to take decades before any new drugs produced due to this study hit the market, but at least now they have the clearest picture yet of what regions they can target. The hope is that by knowing which mutations can lead to the development of tumors, doctors will one day profile each patient's cancer genome and start to personalize medicine towards those that are present in the individual. Once they’ve figured out what genes have mutated, they could potentially then tailor the drugs to the cancer.

How the mutations arise in the first place is a little trickier to answer, and still remains largely unknown. Researchers managed to identify 12 types of damage that led to the genes being altered, some of which are related to family history, and at least one of which is related to collateral damage after the body fights a viral infection. However, as ever, more research is needed.