An international research group released on Wednesday the most comprehensive map of cancer genomes to date that scientists say could allow them to detect the earliest triggers of cancer years in advance.

Their study examined over 47 million genetic changes in over 2,500 human tumours from 38 types of cancers and found that 20 per cent of the cancer-linked mutations are “early events” that occur years ahead of tumour development.

The findings, published in the journal Nature, suggest that nearly half of these early-stage mutations occur among the same set of nine genes, implying that a small number of genes drive early cancer development.

“For over 30 cancers, we now know what specific genetic changes are likely to happen and when these are likely to take place,” said Peter Van Loo, a group member and leader at the cancer genomics laboratory at the Francis Crick Institute in the UK.

“Unlocking these patterns means it should now be possible to develop new diagnostic tests that pick up signs of cancer much earlier,” Van Loo said in a media release accompanying the series of the research papers.

The scientists found that no matter what type of cancer they examined, on average only four to five mutations in cancer cells were so-called “driver mutations” that push cells down the pathway towards cancer.

“It is surprising that almost all have the same number of driver mutations,” said Jakob Skou Pedersen, a collaborator at Aarhus University in Denmark. “However, this is consistent with theories that a cancerous tumour needs to change a certain number of mechanisms in cells before things start to go wrong.”

The scientists are hoping their findings will translate into clinical applications — for early diagnosis and treatment.

“If you know which mutations have caused cancer, the so-called driver mutations, you will be able to better tailor a treatment with the most suitable drugs or design new drugs against the cancer,” Pedersen said. “Precision medicine is completely dependent on mapping the driver mutations in each cancer.”

The study identified ovarian cancer and two types of brain tumours — glioblastoma and medulloblastoma — among types of cancers in which the mutations occur early.

“Some of these genetic changes appeared to have occurred many years before diagnosis, before any other signs that a cancer may develop even in apparently normal tissue,” said Clemency Jolly, a research scholar at the Francis Crick Institute.

The research is part of a global collaborative effort called the Pan Cancer Analysis of Whole Genomes, the largest study of whole cancer genomes involving more than 1,300 scientists from 37 countries.