Unlocked: The genetic secrets behind pancreatic and brain cancer that could open door to new treatments

In the biggest study of its kind, researchers have found dozens of broken, missing and overactive genes that trigger the growth of potentially lethal tumours of the brain and pancreas.

The results help to explain why the cancers are so hard to treat with conventional drugs. They also open the door to new tests and drugs to stop the diseases in their early stages.

Unlocked: Two teams of scientists worked on the impact of defective genes on pancreatic and brain cancer

Cancers arise from changes that accumulate in cells' DNA over the course of someone's life. The changes can eventually lead to a cell's uncontrolled growth.

The new study - which involved researchers from 18 universities and institutions - decoded the DNA of brain and pancreas tumour cells taken from more than 40 patients.

The findings suggest that a conventional war on cancer is unlikely to succeed, according to US expert Prof Kenneth Kinzler, one of the researchers involved.

'The landscape of human cancers is clearly more complex than has been previously appreciated,' said Prof Kinzler, from Johns Hopkins Medical Institutions in Baltimore, Maryland.

'Fighting it is going to be more of a guerilla war than a conventional one because there are dozens of mutated genes in each tumour. Individually, these mutations don't seem formidable.

'But working together, they form an enemy that will require us to develop novel strategies to combat them, and the best long-term strategy may be early detection of tumours, when the number of guerilla warriors is still small and more easily handled.'

Deadly: Around 4,500 brain tumours are diagnosed each year in the UK and most people die within 14 months of diagnosis

Two teams looked at pancreatic cancer and the most common and dangerous form of brain cancer, glioblastoma multiforme (GBM).

Their results were published today in online versions of the journals Science and Nature.

One team of scientists - which included Prof Kinzler - analysed the DNA of more than 20,000 genes from 24 pancreatic and 22 brain tumours.

They found around a dozen chemical pathways in cells which contribute to the development and growth of the cancer. They also found 83 gene mutations involved in pancreatic cancer and 42 in glioblastoma.

Members of the second team, focused on brain cancer and analysed 623 genes from 91 tumours.

They identified some genes known to cause cancer but whose role had previously been underestimated along with genes not previously known to contribute to the disease.

Co-author Dr David Wheeler, Washington University School of Medicine in St Louis, Missouri, US, said: 'Studies like this show the breadth of mutation across many genes. We can see the mutations in all the genes of each pathway that control growth, replication and death in the cancer cell.

'Researchers have never seen the whole landscape like this before, and it's providing many new insights into strategies to diagnose and treat cancer.'

Pancreatic cancer is the 10th most common cancer in Britain and mostly affects people in middle and old age.

Around 7,400 people are diagnosed with the disease each year - usually too late for effective treatment, meaning most people are given a diagnosis of less than a year to live.

The actor Patrick Swayze was diagnosed with the condition earlier this year.

Around 4,500 brain tumours are diagnosed each year in the UK. Glioblastoma is the most common and aggressive variety.

The cancer grows quickly and most people die within 14 months of diagnosis.