Mapping the types and causes of cancer

Cancer is a family of related diseases caused by the uncontrolled division of cells known as a tumour. The Pan-Cancer Analysis of Whole Genomes, a six-year project comprising the work of more than 1,300 researchers in 37 countries, is the largest, most in-depth analysis of cancer genomes to date. It aims to investigate these genetic mutations in more than 30 cancer types with previously unknown causes. 

When researching the causes of a cancer type, the traditional method has been to examine the genetic mutations in the exome, the protein-coding genes that make up one per cent of our genome. However, in the new initiative, scientists decided to study the other 99 per cent of our DNA that is composed of non-coding genes and their mutations. 

The scientists aimed to sequence the entire genome of 38 different tumour types by examining 2,605 localized primary tumours and 173 metastases, tumours that have migrated to other parts of the body. The project thus provided insight into genetic mutations that occur within the non-coding genes of the genome of cancer patients. 

Researchers found that while mutations in coding regions of DNA are central in driving the development of cancers, mutations in the non-coding regions actually contribute as well. Although individually these mutations do not have a great effect, the sum of all these mutations significantly contributed to cancer development, contrary to what was previously believed by scientists. This new information could provide an alternative view on the causes of cancers and pave the way for more targeted gene therapies.

As of February 2020, the team of researchers have published more than six papers in Nature Magazine and an additional 16 papers on other platforms. With such large-scale data-sharing, however, significant measures had to be taken to respect data protection regulations. Mark Phillips, an academic associate at McGill’s Centre of Genomics and Policy, was in charge of implementing the safeguards for the privacy of patients who contributed their data to the study. 

“From the perspective of the participants themselves, genomic data [are] extremely rich and usable for a multitude of purposes,” Phillips wrote in an email to The McGill Tribune. “[They are] often also stored alongside other sensitive health information, such as a participant having a certain disease [….] Genomic data […] potentially [tell] so much about a person that […] there are any number of additional possible ways the data could be used or misused that no one has conceived of yet.”

The Pan-Cancer Project’s results relied heavily upon patient data and data sharing. In fact, privacy laws play a big part in any human genomics project. 

“We should aim for as universal as possible of a code of conduct for genomic data sharing,” Phillips wrote. “Genomics has become a coherent, international field of study. It’s also more given to close international collaboration and data-sharing than other fields of research, and so a shared framework across this new field is particularly needed.” 

Without patient data and the work of researchers like Phillips who ensure that they remain secure, the project itself would not have been possible.

The study also highlighted the notable use of carbon dating to study cancer genetics, a method based on retracing cancer-causing mutations that had occurred several years before the tumour’s appearance. Using this method, the researchers found that 20 per cent of these mutations occurred before the first trace of a tumour, and that a large proportion of these mutations were within the same group of genes. Thanks to patient data and a diverse team of researchers, the study’s results may shape future methods of early-on cancer detection, allowing for doctors to find cancers before they progress.

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