Lung cancer may have spread to other parts
of the body by the time it is diagnosed
Experimental drugs already used to treat breast cancer may also fight lung cancer, research reveals.
Non-small-cell lung cancer (NSCLC), the commonest type of lung cancer, is the leading cause of cancer deaths worldwide. Few drug treatments exist.
Scientists at the Institute of Cancer Research in London discovered breast cancer drugs called PARP inhibitors worked in up to half of NSCLC tumours.
In the lab, the drugs killed cancerous cells and left healthy ones intact.
Experts say more studies and clinical trials are needed, but they were excited by this early work, which will be published soon in the journal Oncogene.
Study author Dr Chris Lord said: "This study suggests that PARP inhibitors, treatments already in clinical trials to treat breast and ovarian cancer, could also be a promising treatment for patients with certain forms of lung cancer.
"Lung cancer is hard to treat and unfortunately has very poor survival, so there's an urgent need to find new treatments.
'Save more lives'
"Our research opens up an exciting new route, by showing how we could repurpose drugs originally designed for use against other forms of cancer."
Dr Harpal Kumar, of Cancer Research UK, which funded the work, said: "Lung cancer is the UK's biggest cancer killer but it's proven to be one of the hardest cancers to study and survival rates remain poor.
"We're making substantial investments in lung cancer research to discover better ways to diagnose and treat the disease. Our hope is that studies like this will lead to more effective treatments for lung cancer patients and ultimately save more lives."
Lung cancer is the most common cause of cancer death in the UK, accounting for more than a fifth of all cancer deaths.
More than eight out of 10 cases of lung cancer are NSCLC - more than 33,000 cases per year in the UK.