London: Winning the battle against cancer seems far from reality, as a new study led by an Indian-origin scientist has claimed that millions of people carry tumours which still go undetected for a decade.
Currently available blood tests help identify cancers by the presence of substances they secrete into the bloodstream.
But, the new study led by Prof Sanjiv Gambhir of Stanford University in the US showed that it could take a cancer cell a decade or even longer to grow into a tumour and begin shedding enough of these biomarkers to be picked up in a screening.
Many biomarkers made by tumour cells are also produced naturally in a healthy body, so it can take years before they reach a high enough concentration to cause concern, the Daily Telegraph reported.
More sensitive tests and more distinctive biomarkers must be found to bring about earlier diagnoses of cancer, which are key to the success of any treatment, the researchers said.
"It`s really important for us to find biomarkers that are made exclusively by tumour cells, said Prof Gambhir.
"The good news is that we have potentially 10 or even 20 years to find the tumour before it reaches this size, if only we can improve our blood-based methods of detecting tumours."
The study, reported in the Science Translational Medicine journal, is the first to connect the size of a tumour with the level of biomarkers it releases into the bloodstream.
It found that an ovarian tumour could reach the size of 1.7 billion cells before being detected by the current tests. It would be the size of a 2cm cube and would have been present in the body for between 10 and 13 years before high levels of its most distinctive biomarker became unusually high, they said.
In theory, a similar biomarker which was not produced elsewhere in the body could be detected within eight years, when the tumour would be the size of a four millimetre cube.
Early detection is seen as the key to beating most types of cancer, with 90 per cent of ovarian cancer patients surviving if their tumour is detected at an early stage.
But more than 80 per cent of patients are not diagnosed until the late stages of the disease, by which point their chances of living for another five years are less than three in ten.
The researchers built their model by calculating how fast particular tumours grow from a single cell, how much of a particular biomarker they release each hour and how much biomarker they must have produced for it to stand out from normal levels in current tests.
Two years ago, a study by a separate team at Stanford found that existing tests for ovarian cancer were unable to detect tumours early enough to significantly alter the mortality rate.