It appeared in every type of breast cancer they examined and other forms of the disease including prostate and bowel cancer, as well as the blood cancer lymphoma.
Researchers have developed a test that could be used to diagnose all cancers.
A blood test can detect cancer within just 10 minutes, scientists have found, raising hopes that hard-to-spot diseases could be picked up early when treatment is most effective. "This is a huge discovery that no one has grasped before", said Carrascosa.
The scientists are now working towards clinical trials with patients who have a broader range of cancer types than they have tested so far.
It is based on a process known as epigenetics - the attachment of a chemical tag known as a methyl group to DNA. This modification prevents certain genes from being expressed. Altering this pattern is one of the ways cancer cells regulate their own proliferation. While the DNA inside normal cells has methyl groups dotted all over it, the DNA inside cancer cells is largely bare, with methyl groups found only in small clusters at specific locations.
The researchers have dubbed it the cancer "methylscape" - for methylation landscape.
"If it's very sensitive, we could use it for early diagnosis of cancer ... especially for cancers where there is no screening paradigm, like ovarian and pancreatic", she said.
Researchers have always been looking for a commonality among cancers to develop a diagnostic tool that could apply across all types.
Professor Trau said the team discovered that intense clusters of methyl groups placed in a solution caused cancer DNA fragments to fold into unique three-dimensional nanostructures that could easily be separated by sticking to solid surfaces such as gold. These were different to what we saw with normal tissue DNA in the water. If cancer DNA is present, the gold nanoparticles will turn a different color than if cancer DNA is not present.
Ged Brady, of the Cancer Research UK Manchester Institute, said: "This approach represents an exciting step forward in detecting tumour DNA in blood samples and opens up the possibility of a generalised blood-based test to detect cancer".
The researchers have tested their technology on about 200 samples from cancer patients and healthy people, finding that the test was up to 90 percent accurate in detecting cancer.
Sina said: "It works for tissue-derived genomic DNA and blood-derived circulating free DNA". He added that larger studies are needed to evaluate the accuracy of the test, as well as whether it could be useful for patients, compared with existing tests.
"It seems to be a general feature for all cancer". But she added that the study was "very proof of principle at this point".
Blood tests are sometimes ordered to help doctors diagnose cancer, but different ones are required depending on the type suspected. It's also unclear exactly how high the levels of cancer DNA need to be in order for the test to work, which would affect how early in the course of the disease the test could be used, the researchers said.
In its current form, the test would be less applicable as a screening test, given that it can not detect types of cancer, Ohm told Live Science.
Co-author Professor Matt Trau, from the University of Queensland, said: 'We certainly don't know yet whether it's the Holy Grail for all cancer diagnostics, but it looks really interesting as an incredibly simple universal marker of cancer, and as a very accessible and affordable technology'.
"But it looks really interesting as an incredibly simple universal marker of cancer, and as a very accessible and low-cost technology that does not require complicated lab-based equipment like DNA sequencing".