This is the first review of studies to measure the effects of continued smoking after diagnosis of lung cancer and suggests that it may be worthwhile to offer smoking cessation treatment to patients with early stage lung cancer.
Worldwide, lung cancer is the most commonly diagnosed form of cancer. In the UK, it is second only to breast cancer, accounting for around 39,000 new cancer diagnoses annually.
Smoking increases the risk of developing a primary lung cancer; lifelong smokers have a 20-fold increased risk compared with non-smokers. But it is not known whether quitting after a diagnosis of lung cancer has any benefit.
So researchers at the University of Birmingham analysed the results of 10 studies that measured the effect of quitting smoking after diagnosis of lung cancer on prognosis.
Differences in study design and quality were taken into account to minimise bias.
They found that people who continued to smoke after a diagnosis of early stage lung cancer had a substantially higher risk of death and a greater risk of the tumour returning compared with those who stopped smoking at that time. Data suggested that most of the increased risk of death was due to cancer progression.
Further analysis found a five year survival rate of 63-70% among quitters compared with 29-33% among those who continued to smoke. In other words, about twice as many quitters would survive for five years compared with continuing smokers.
These findings support the theory that continued smoking affects the behaviour of a lung tumour, say the authors. They also provide a strong case for offering smoking cessation treatment to patients with early stage lung cancer.
Further trials are needed to examine these questions, they conclude.