## Did you know that...

...a large number of mutations accumulate in tumour cells during the onset and progression of the disease - they can contain hundreds of thousands, sometimes even more than a million mutations. However, only a small proportion of them are directly responsible for the development of cancer; these are called "driver" mutations. The remaining mutations in DNA, called "passenger" genes, are remnants of the cell's experience before cancer development and may not be in the domains of oncogenes or tumour suppressor genes. However, there is also a large group of mutations that arise during the transformation of cells into tumours. These set of mutations in tumour cells is usually referred to as the mutational signature, which can make tumours of the same organ in different patients significantly different from each other. A new study aim to sequence the genomes of 19 tumour types from 12,000 patients and create a genetic signature for each. Individual mutation types can be used to determine whether a person has had a sunburn or been exposed to cigarette smoke, for example, and then used to clarify the cause(s) of a particular type of cancer. The authors of the study liken the mutation signature to a sandy beach full of footprints. If you know what you are looking for, you can learn a lot about who was on that beach and what happened there. For example, the study was able to uncover 58 new signatures, which means 58 causes of cancer that we do not yet understand. At the same time, by comparing mutations across genomes it was possible to determine the type of tumour, or if the tumour was causes by an inherited mutation or a random type of disease. In addition, mutation signature data can indicate an appropriate therapeutic target and thus be a useful tool for personalized medicine.