Scientists have found a gene in a primitive worm that may give vital clues about the development of cancer.
Nematodes are useful scientific tools
The gene, in the nematode worm, is similar to the human breast and ovarian cancer gene BRCA1.
BRCA1 is known to stop cancer by repairing damaged DNA, but how it does this is not known.
The latest research, by Cancer Research UK and published in Current Biology, may lead to an answer - and new treatments.
Previous studies have focused on simple organisms such as yeast, worms and flies for a gene similar to BRCA1 but have found nothing.
And previous studies on the nematode worm had also drawn a blank.
Dr Simon Boulton, from the Cancer Research UK London Research Institute,
said the new finding was surprising - but very exciting.
He said: "It's nearly a decade since the BRCA genes were discovered and implicated in the development of breast and ovarian cancer but we are still very much in the dark about how they function.
"The detailed genetic analysis we can do in cells of the worm is not really possible in more complex human cells."
The soil-dwelling nematode has less than a thousand cells and is around one millimetre in length.
But, like us, it develops from embryo to adult and has a gut, nerves, muscles and skin.
We also once shared a common ancestor so around 40% of its genes are closely related to ours.
Dr Boulton said: "Even though the worm set off on a different evolutionary path to us hundreds of millions of years ago, scientists can compare the worm and human genome to identify related genes.
"They can then use the simpler worm system to examine their function. It's a fast and easy way to address some bigger questions about humans."
The researchers found BRCA1 works in tandem with another gene BARD1 in the worm, in much the same way as the two genes interact in humans.
By switching off the two genes and exposing the worms to cancer-causing radiation, they were able to prove that they play a key role in DNA repair.
Professor Robert Souhami, director of clinical and external affairs at Cancer Research UK, said: "Studying the BRCA1 counterpart in the worm will accelerate our understanding of how defects in this gene can lead to breast cancer and in the future will offer possibilities for prevention and treatment."