Scientists in the US have discovered that heavy smokers who develop lung cancer could have up to 50,000 genetic mutations in affected tumours.
A team from Roche's Genentech biotechnology unit in California found that, upon analysis, a tumour belonging to a 51-year-old man who had smoked an average of 25 cigarettes a day for 15 years contained as many as 50,000 genetic mutations - one for every three cigarettes smoked.
The results were so unexpected that the team carried out further checks to ensure their findings were correct and investigated the patient's background to see if there was anything unusual about his lifestyle that could have contributed to the results.
"Fifty thousand is a huge number. No one has ever reported such a high number," said Zemin Zhang of Genentech, whose findings appear in the journal Nature.
The research team used gene sequencing technology which allowed them to study entire genomes rather than a select sample of genes that are important in certain forms of cancer.
The team also found that areas of the genome responsible for producing proteins that are vital to cancer cell survival are less susceptible to genetic mutations, suggesting that they are better protected.