Stress kills, doctors often say. And, now a new study has claimed that it can cause cancer as it aids the growth of tumour cells.

Experts had suspected that stress was involved in the development of cancer, but had no biological evidence. Earlier studies failed to establish any link between the condition and the disease.

Now, an international team has found that it may not necessarily be the emotional stress, but could be physical stress or even the stress which occurs in people's bodies as they fight infection and this may lead to cancer.

The study has revealed mutant genes that are primed to turn cancerous can be made active by stress signals, British newspaper the Daily Express reported.

Lead researcher Prof Tian Xu from Yale University's School of Medicine said: "A lot of different conditions can trigger stress, signalling physical stress, emotional stress, infections, inflammation - all these things. Bad news for cancer."

For their study, the researchers focused on the activity of two mutant genes known to be involved in human cancers.

One, called RAS, has been involved in 30 per cent of cancers. The other, tumour-suppressing gene called "scribble", allows cancers to develop when it becomes defective. Neither can cause cancer on its own.