Human body comprises of about 10 trillion cells, which divide and make new cells in a controlled fashion. This information is encoded in the DNA which forms the Genome. The human body hence grows and repairs. The genome can be thought of as the instructions for running a cell. It tells the cell what kind of cell to be – is it a skin cell or a liver cell? It also has the instructions that tell the cell when to grow and divide, and when to die.
When a cell divides to become two cells, the genome is copied. Sometimes when the cells divide, mistakes happen when copying the genome. These mistakes are called are called mutations. Mutations are caused by natural processes in our cells, or just by chance. They can be caused by external factors in our environment too – like radiation from sunlight.
Usually, cells can repair mutations in their genome. In fact most DNA damage is repaired immediately, with no ill effects. If the damage is very bad, cells may self destruct instead. Or the immune system may recognize them as abnormal and kill them. This helps to protect us from cancer. But sometimes mutations in critical genes mean that a cell no longer understands its instructions, and starts to multiply out of control. It doesn’t repair itself properly, and it doesn’t die when it should. The abnormal cell keeps dividing and making more and more abnormal cells. These cells form a lump, which is called a tumour. This is how Cancer grows in the body.
Cancer whole genome sequencing allows us to detect two types of changes, germline mutations and somatic mutations.