Research has suggested that determining the number of lung cancer cells circulating in a person's blood could determine how aggressive the cancer is.
The study, published in the Journal of Clinical Oncology, suggested that this data could then be used to predict the best treatment course to use for the individual concerned.
Circulating tumour cells (CTCs) in blood samples of 101 non small cell lung cancer patients were studied and counted before and after one cycle of chemotherapy.
Those with five or more CTCs had a significantly worse survival rate.
Dr Fiona Blackhall, joint author and lung cancer clinician, commented: "Our research shows a new way to monitor how a patient's lung cancer is responding to treatment and determine how aggressive it is.
"We now need to test our findings in more patients but, if our results are confirmed, there is now the potential to tailor treatments to individual patients and find new ways to treat the disease."