U.S. and Canadian researchers have taken steps toward developing a gene test to determine whether a patient's lung cancer is especially aggressive, or whether radical treatment can be avoided.

The researchers reported on Sunday that they analysed lung cancer tissue from 442 people to confirm that measuring the activity of certain genes can help predict early on which cases may be the most deadly and which have a better prognosis.

Knowing whether a person has an aggressive tumour - one likely to spread quickly and uncontrollably beyond the lungs - is critical in determining the type of treatment needed.

The researchers said tracking gene activity, along with taking into account clinical factors like the patient's age, sex and the tumour stage - for example, whether it had spread - made them better able to make a prognosis.

Doctors are eager to come up with reliable ways to determine how aggressive a tumour is likely to be when a patient is in the earliest stages of lung cancer. Some patients have aggressive tumours that could require additional types of potentially onerous treatment, while people with less invasive tumours may be able to avoid such treatment.

"We're hoping that by looking at activity of specific genes that it would basically give us a window into the aggressiveness of it," David Beer of the University of Michigan Medical School, who helped lead the study published in the journal Nature Medicine, said in a telephone interview.

Lung cancer is the leading cause of cancer death in men worldwide and the second leading cause of cancer death in women, with about 975,000 men and 376,000 women projected to die from it annually, according to the American Cancer Society.

Out of about 22,000 genes tracked in the study, Beer said the activity of "hundreds" of them was implicated in predicting the aggressiveness of a tumour.

"We're assuming that the genes that we're looking at are playing a role in the aggressive behaviour of the tumours - so their ability to invade and metastasize (spread)," he said.

Patients whose lung cancer has not spread may not need additional treatment after surgery to remove the tumour.

But if it can be shown a tumour is likely to be aggressive, the patient could be a candidate for getting further therapy that might include chemotherapy and radiation.

The goal is for a simple test assessing the activity of certain genes to determine the aggressiveness of a tumour. The researchers said they plan to refine the process, identifying critical genes and testing more tissue samples.

Beer said he is optimistic that a predictive test can be developed "relatively soon."

"We're working on it right now and so are lots of people around the world. I think within the next five years we'll definitely have something," Beer added.

The lung cancer tissue samples came from six different institutions in the United States and Canada.

The particular type of cancer involved in the study was lung adenocarcinoma, which often is caused by smoking.