Signs of cancer can appear long before diagnosis, study shows

[nitpicker]

https://www.theguardian.com/science/2020/feb/05/signs-of-cancer-can-appear-long-before-diagnosis-study-shows

Signs of cancer can appear long before diagnosis, study shows

Hannah Devlin Science correspondent

Wed 5 Feb 2020 18.20 GMT Last modified on Thu 6 Feb 2020 01.05 GMT

Early signs of cancer can appear years or even decades before diagnosis, according to the most comprehensive investigation to date of the genetic mutations that cause healthy cells to turn malignant.

The findings, based on samples from more than 2,500 tumours and 38 cancer types, reveal a longer-than-expected window of opportunity in which patients could potentially be tested and treated at the earliest stages of the disease.

The work was carried out as part of the Pan-Cancer Analysis of Whole Genomes project, the most comprehensive study of cancer genetics to date.
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The discovery that the seeds of cancer are often sown many years before the first symptoms arise will not change cancer screening in the immediate term. But it points to the possibility that those at risk could be spotted far earlier.

The study revealed that about half of the earliest mutations occurred in just nine genes, meaning there is a relatively small pool of common genes that serve as triggers for cells to diverge from healthy development to a path towards cancer. It might be possible, in future, to pick up such mutations using so-called liquid biopsies – genetic tests that detect mutations in free-floating DNA carried in the blood that can indicate the presence of tumours elsewhere in the body.
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The team analysed and sequenced nearly 2,700 whole genomes of cancer samples and mapped mutations in 38 different types of tumours.

While human cells undergo billions of mutations, only a small number of them, called driver mutations, give rise to cancer. The researchers looked at how many times a single change, or driver mutation, had been replicated and copied across chromosomes.

Using what they describe as a “carbon-dating method”, they were able to reconstruct the order in which the genomes of cancer cells started to accumulate errors and eventually carry large segments that had been scrambled or copied. The team found that these mutations occurred “particularly early” in ovarian cancer as well as in two types of brain tumour, glioblastoma and medulloblastoma.

The analysis is published in Nature as part of a wider collection of 22 papers from the Pan-Cancer project.
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