In this explainer episode, we’ve asked Dr Katie Snape, principal clinician at Genomics England, cancer geneticist, and specialist in inherited cancer, to explain how genomics can help us understand cancer.You can also find a series of short videos explaining some of the common terms you might encounter about genomics on our YouTube channel.If you’ve got any questions, or have any other topics you’d like us to explain, let us know on [email protected].You can download the transcript or read it below.Flo: How can genomics help us understand cancer?  I'm Florence Cornish, and today I'm joined with Katie Snape, who is Principal Clinician here at Genomics England, lead Consultant for Cancer Genetics at the Southwest Thames Centre for Genomics, and Chair of UK Cancer Genetics Group.So Katie, it's probably safe to say that everyone listening will have heard the word cancer before. Lots of people may have even been directly affected by it or know someone who has it or who has had it, and I think the term can feel quite scary sometimes and intimidating to understand. So, it might be good if you could explain what we actually mean when we say the word cancer.  Katie: Thanks, Florence. So, our bodies are made up of millions of building blocks called cells. Each of these cells contains an instruction manual, and our bodies read this to build a human and keep our bodies working and growing over our lifetimes. So, this human instruction manual is our genetic information, and it's called the human genome.Throughout our lifetime, our cells will continue to divide and grow to make more cells when we need them. And this means that our genetic information has to contain the right instructions, which tell the cells to divide when we need new cells, like making new skin cells, for example as our old skin cells die, but they also need to stop dividing when we have enough new cells and we don't need anymore. And this process of growing but stopping when we don't need anymore cells, keeps our bodies healthy and functioning as they should do.However, if the instructions for making new cells goes wrong and we don't stop making new cells when we're supposed to, then these cells can grow out of control, and they can start spreading and damaging other parts of our body. And this is basically what cancer is. It's an uncontrolled growth of cells which don't stop when they're supposed to, and they grow and spread and damage other tissues in our body.Florence: So, you mentioned there that cancer can arise when the instructions in our cells go wrong. Could you talk a little bit more about this? How does it lead to cancer?Katie: Yeah. So the instructions that control how our cells should grow and then stop growing are usually called cancer genes. So our body reads these instructions a bit like we might read an instruction manual to perform a task.So if we imagine that one of these important cancer genes that has a spelling mistake, which means the body can't read it properly, then those cells won't follow the right instructions to grow and then stop growing like they should. So if our cells lose the ability to read these important instructions due to this type of spelling mistake, then that's when a cancer can develop. As these spelling mistakes happen in cancer genes, we call them genetic alterations or genetic variants.Florence: And so, when you're in the clinic seeing somebody who has cancer, what kinds of genomic tests can they have to help us find out a little bit more about it?Katie: So the genetic alterations that can cause cancer can happen in different cells. So that's why cancer can affect many different parts of the body. If a genetic alteration happens in a breast cell, then a breast cancer might develop. If the alteration happens in a skin cell, then a skin cancer could develop. We can take a sample from the cancer. This is often known as a biopsy, and then we can use this sample to extract the genetic informat