Lung cancer should no longer be seen as a “smokers’ disease” because one in five new cases has nothing to do with the habit, the chief executive of Cancer Research UK has said.

A drop in the number of smokers means that fewer are developing lung cancer, but the number of people who contract the disease from other causes, such as asbestos, remains steady at about 6,000 per year in the UK.

It means that while smoking is still the leading cause of lung cancer, the proportion of non-smoking related cases is growing larger over time.

Speaking at the launch of a major genetic study of the disease on Wednesday Dr Harpal Kumar said: “It is not so long ago that we used to say more than nine in ten lung cancers were smoking-related, and now we say eight in ten.

“People tend to think it is just a smokers’ disease, but it isn’t,” he added. “It is a significant problem, and one that is growing globally.”

While scientists have made major improvements in diagnosis and treatment for breast and other cancers in recent years, there has been virtually no improvement in lung cancer survival rates since 1970.

Along with problems like the typically late diagnosis of lung cancer, which makes it harder for researchers to obtain biopsies for studies and recruit patients to trials, the perception of the condition as a problem for smokers could be one reason why progress has been so slow, Dr Kumar said.

The new £14 million study launched on Wednesday is aimed at tracking the genetic changes which trigger the growth of tumours and help them develop resistance to drugs.

Genetic mutations are known to drive the development of cancer, but are also the target of drugs aimed at stopping tumours in their tracks.

The project, one of the largest ever studies of lung cancer patients, will focus on how tumours continue to develop new mutations as they grow, making them genetically complex.

Their continued evolution means all cells in a tumour do not share the same characteristics and are often quite different - a major problem which has hindered progress in developing new drugs for the disease.

Over the course of nine years scientists will analyse thousands of tumour biopsies from 850 patients across the UK, examining the genetic differences within individual tumours and between different patients.

Identifying which mutations occur first, and are therefore shared by the largest proportion of cells in a tumour, could allow doctors to select the drug with the biggest potential impact for each individual patient.

Prof Charlie Swanton of Cancer Research UK’s London Research Institute and University College London, who is leading the study, said: “Success in treating lung cancer has been difficult to achieve but we’re hoping to change that.

“The first step to improving cancer diagnosis and treatment is to understand more about the disease and how it changes over time.”

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By Nick Collins, Science Correspondent