Key points from article :
A major study analysed data from nearly 3 million Koreans, finding that quitting smoking for at least 15 years halved the risk of developing cancer.
Those who quit before 50 saw the biggest reduction in lung cancer risk (57%), compared to those who continued smoking.
The longer you smoke, the higher your cancer risk, but quitting still offers benefits even later in life.
Lung cancer risk dropped 42% for quitters, while other cancers like liver and colorectal saw smaller reductions.
Smoking is the leading preventable cause of cancer in the UK, responsible for 1 in 4 deaths.
The study was conducted at the National Cancer Center near Seoul, South Korea and was published in the Jama Network Open.