A recent study from MIT, Harvard, and elsewhere found early signs of cancer can appear years before diagnosis.
Developing tests for these genetic signs could provide new ways to spot cancer early.
The study is published in Nature. One author is Peter Van Loo, a group leader in the Cancer Genomics Laboratory at the Crick.
The team looked at 47 million genetic changes in more than 2,500 human tumors, across 38 cancer types.
By looking at how many times a single change had been replicated and copied across chromosomes, the researchers were able to determine the order in which they happened and the relative timing between them.
Using this method, they found that just over 20% of mutations can be considered early events in a tumor’s development, with some of these changes taking place years, even decades, before the cancer is found.
Of these early mutations, half fall within the same nine genes, meaning there is a small number of genes that are common drivers of early cancer development.
For more than 30 cancers, the team now know what specific genetic changes are likely to happen, and when these are likely to take place.
The research identified cancer types in which mutations tend to happen particularly early, for example, ovarian cancer and two types of brain tumors, glioblastoma and medulloblastoma.
It also revealed the specific changes that are likely to happen early in each of the more than 30 cancer types.
One of the most common early changes in many cancers, including ovarian cancer, affects a gene called TP53.
In glioblastoma, an extra copy of chromosome 7 is very frequently gained early, while for pancreatic neuroendocrine cancer a number of chromosomes are lost in the initial stages of tumor development.
The team says some of the genetic changes appear to have occurred many years before diagnosis, long before any other signs that cancer may develop, and perhaps even in apparently normal tissue.
They also found the cancers that are likely to have many different mutations enter their DNA at the same time, as well as the timing of these events and the genes likely to be affected.
This process was found to be an important and critically early event in the evolution of most cancers, particularly in melanomas.
The team hopes the findings could help develop new diagnostic tests, that pick up signs of cancer much earlier.
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