One particular molecule, called RAD51D, appeared repeatedly at the site of the telomeres, suggesting it was interacting in some way with the timer mechanism.
When researchers blocked the activity of RAD51D they found substantial damage to the telomeres and other parts of the genome - the telltale signs of accelerated ageing.
They suggest this shows that the molecule usually acts as a protective "cap" for the telomeres in cancer cells, preventing the normal telomere shortening.
To understand why this could be so important:
Dr Madalena Tarsounas, who led the study, said: "Cancer has an amazing ability to shake off the shackles of ageing and death, which is one of the reasons why it can be so hard to treat.
"Understanding how cancer cells remain eternally young has been a key focus of research for more than a decade, so it's particularly exciting to have made such a striking discovery."
She added: "We have found evidence of a completely new mechanism for stopping the clock on a cancer cell's timer and preventing its lifespan from ticking down.
"It raises the possibility of starting the clock again and making cancer cells susceptible to death once more."
She added: "As well as opening the way to new types of treatment for cancer, our study has shed light on the complex but intriguing processes which control how and when we get old."