The mutations that cause deadly brain tumors appear to take root years, or even decades, before a cancer diagnosis.

Brain tumors, like any cancer, result from mutations in the body’s own DNA, which cause out-of-control growth of cells. In other words, brain tumors are not caused by an external factor like a bacteria or virus, and the difficult reality is that there is little a person can do to prevent a brain tumor. What’s more, there are no major known lifestyle factors that contribute to brain tumors the way there are with, say, lung cancer and smoking.

A corollary of this is that if you are facing a brain tumor, its important to remember that it’s not your fault, and however you approach your fight, you can do it free of guilt or shame.

That said, many people still want to know why this happen to them. Some people in our community have offered wisdom and reflection on such questions, which we offer below. But we can also offer a little bit of insight into what happens biologically that leads to a brain tumor.

A brain tumor starts with a mutation. And just what does that mean? Part of what makes your body function, grow, heal, and adapt is a continuous process of cells replicating and dividing. Cells contain a set of instructions at their center, encoded in a strand of DNA. When a cell divides, that DNA gets copied and two new cells result, one with the original DNA and one with the copy, and the process repeats. However, sometimes the copy isn’t perfectly accurate. It has errors. These errors are what we mean when we say mutation. As the cycle turns, mutated DNA gets copied and passes the errors along.

One common type of mutation damages the instructions that tell a cell that it should grow and divide no further. This type of mutation would be called pre-cancerous.

Scientists have long suspected that these pre-cancerous mutations happen years or even decades before a cancer diagnosis, and there is a growing body of evidence that this is true.

As Brains for the Cure has written in the past, potential cancers pop up all the time but most of the time your immune system tracks them down and eliminates them before they can gain a foothold. But once a brain tumor does get established, a number of changes occur that makes it difficult to dislodge, either by the body’s own systems or with treatment.

However, if pre-cancerous mutations pop up years before tumors do, and if they are more easily destroyed early on, this means that scientists may be able to create early detection systems that allow us to detect problems before they become cancerous tumors.

A major study published in Nature last month used massive computational data processing of over 2,500 tumors across 38 different tumor types (including brain tumors) to identify the mutations that led to cancer. Researchers found that a small number of “cancer-driver” mutations were shared in common across all tumors. Furthermore, in brain tumors like glioblastoma and medulloblastoma, these mutations occurred “particularly early.”

One of the lead authors of the study told The Guardian newspaper that “unlocking these patterns means it should now be possible to develop new diagnostic tests that pick up signs of cancer much earlier.” And as such diagnostic tests are developed and become widespread, there is reason to hope that patients who are at risk of developing glioblastoma or another aggressive brain tumor could be monitored much more closely with imaging, and could potentially catch brain tumors at a stage where complete removal and successful treatment is much more probable.