Pancreatic cancer may lurk in the body for decades before the patient falls ill, according to a new finding that could lead to early diagnosis and treatment of the disease which kills patients in 95 per cent of cases.

Genetic analysis of tumours by researchers at the Howard Hughes Medical Institute and Johns Hopkins University in the U.S. suggested that the first mutations may happen 20 years before they become lethal.

Pancreatic cancer, a malignancy in pancreas or the human digestive system, is often aggressive and unresponsive to treatment by the time it is diagnosed.

Researcher Dr Bert Vogelstein of Howard Hughes Medical Institute said there had been two theories about why these tumours were so lethal -- either that they were highly aggressive from the start or that they were so advanced at the time of diagnosis, that little could be done.

“But we were surprised and pleased to discover that this second theory is correct, at least for a major fraction of tumours,” Dr Vogelstein was quoted as saying by the BBC News.

“It means that there is a window of opportunity for early detection of pancreatic cancer.”

For their research, the scientists looked at tissue samples, both from the “primary” tumours in the pancreas and from other parts of the body to which the cancer had spread, called “metastatic” tumours.

The DNA in every gene of these tumours was sequenced, looking for signs of mutations -- points at which the genetic code has changed.

On average each metastatic tumour had 61 cancer-related mutations. Two-thirds of these had been present in the original pancreatic tumour.

Because such genetic mutations occur at a relatively steady rate, this accumulation of mutations offers an insight into just how long the cancer had been developing and growing at each stage.

Using this “molecular clock”, the researchers estimated that on average, it took 11.7 years for a single gene mutation in a pancreas cell to become a “mature” pancreatic tumour.

From this point, an average of another 6.8 years elapsed before cells from the pancreatic tumour formed a tumour in another organ.

However, once this stage had been reached, less than three years passed before the patient died. So, from start to finish, the development of the disease took more than 20 years on average, the researchers reported in the journal Nature.

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