Smokers who are diagnosed with early stage lung cancer can roughly double their chances of being alive five years later by giving up smoking, researchers say. However, many people with lung cancer are diagnosed at a later stage, and there’s very little research on whether these people would benefit from quitting.

What do we know already?

The warnings appear on every cigarette packet, often in stark lettering, but sometimes including grisly photos of diseased lungs. Whatever the reasons someone has for smoking, not being aware of the risks is unlikely to be one of them.

Given that many people with lung cancer die within a year of being diagnosed, it would take an insensitive sort of character to lecture a patient on their smoking habits. Nevertheless, a new study casts some light on the continuing harm someone might be doing to themselves by smoking while being treated for lung cancer.

What does the new study say?

Giving up smoking can help people with lung cancer to live longer, according to a round-up of all the research on the topic. The researchers used a mathematical model to predict life expectancy, based on observing people with lung cancer who chose to either carry on smoking or give up.

The researchers think that someone with a kind of lung cancer called non-small cell, diagnosed at an early stage at age 65, would have a 70 percent chance of being alive five years later if they gave up smoking. The chance of being alive in five years would fall to 33 percent for someone who kept on smoking.

While the predicted difference in life expectancy is large, in practice few people may be in a position to benefit. The majority of people are diagnosed with lung cancer at a later stage. There’s been very little research looking at the implications of smoking for these people.

How reliable are the findings?

The study is a review of all the research that’s been done so far. One weakness is that most of the previous studies have looked at people with early stage cancer.

Another is that most of the existing studies are of the observational kind. In other words, people chose whether to keep smoking or not, and the researchers kept track of what happened to them. This could affect the results. For example, people who’d smoked less in the past might find it easier to give up, so the benefit could come from having less lung damage in the first place, rather than quitting. However, in practice, it seems that it was the least healthy people who were most likely to quit, which would mean the study could underestimate the benefits of giving up.

Where does the study come from?

The study was published in the BMJ (British Medical Journal), which is owned by the British Medical Association. It was carried out by an organisation called the UK Centre for Tobacco Control Studies, with funding from several organisations, including the British Heart Foundation, Cancer Research UK, and the National Institute for Health Research.

What does this mean for me?

In health terms, giving up smoking is almost always likely to be beneficial. However, if you’ve been diagnosed with lung cancer, you’re likely to be facing all sorts of difficult decisions about treatment and about the future. It’s entirely down to you to decide the amount of effort you’re prepared to put into giving up smoking. The Guardian