Quitting Smoking at Any Point Improves Lung Cancer Survival, Study Finds

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People who quit smoking at any time—even 2 years before a lung cancer diagnosis—improve their chances of survival after being diagnosed with the disease, according to the results of a large international study presented by Fares et al in a press briefing in advance of the ASCO20 Virtual Scientific Program (Abstract 1512). 

While much is known about how smoking cessation affects the risk of developing lung cancer, there has been uncertainty about how soon after smoking cessation survival benefits start to accrue after a lifetime of smoking. 

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“This research shows that if you’re a smoker and you quit, no matter when you quit, you will be more likely to survive after being diagnosed with lung cancer, compared to someone who continues smoking,” said lead author Aline Fusco Fares, MD, a clinical research fellow at Princess Margaret Cancer Centre in Toronto. “The study’s message is simple: quit smoking now.”  

About the Study
The researchers analyzed data from 17 International Lung Cancer Consortium (ILCCO) studies that included data on time to smoking cessation. The consortium is an international group of lung cancer researchers who aim to share comparable data from ongoing lung cancer case-control and cohort studies.  

This analysis included 35,428 patients with lung cancer, of which 47.5% were current smokers, 30% were former smokers, and 22.5% had never smoked at the time of diagnosis.  

Key Findings
The study results showed a decreased risk of death after lung cancer diagnosis for former smokers, including deaths from all causes. 

“Although we can’t say that all these deaths after a lung cancer diagnosis are specifically due to the disease, a proportion of them certainly are,” said senior author Geoffrey Liu, MSc, MD, a clinician-scientist at the Princess Margaret Cancer Centre. 

The researchers found that among all former smokers, among those who quit less than 2 years before, between 2 and 5 years before, and more than 5 years before a lung cancer diagnosis had, respectively, a 12%, 16%, and 20% reduced risk of death from all causes when compared to current smokers. The benefit seen from quitting smoking was slightly greater among those who had smoked at least 20 cigarettes per day for more than 30 years. 

There was also a trend toward improved lung cancer–specific survival for those who quit smoking less than 2 years before and between 2 and 5 years prior to diagnosis. Improvement in lung cancer–specific survival was statistically significant for those who quit smoking for more than 5 years prior to diagnosis. 

Lung cancer screening offers an opportunity to encourage smokers to quit. With this in mind, the researchers next looked at long-term, heavy smokers—those who smoked more than 30 pack-years—as these smokers would likely be included in lung cancer screening recommendations. A pack-year is defined as the equivalent of 20 cigarettes (a standard pack of cigarettes) smoked every day for 1 year. 

Long-term heavy smokers who quit less than 2 years before, between 2 and 5 years before, and more than 5 years before their lung cancer diagnosis had 14%, 17%, and 22% respective reduced risks of death from all causes, compared to current smokers. This effect was not as strong for those who smoked less than for < 30 pack-years; the reduction rate was significant only for those who had quit at least 5 years before diagnosis (23%). 

“We saw a slightly bigger benefit to quitting among people who had smoked heavily for over 30 years compared with the overall population of former smokers. For long-term smokers, the benefits of quitting cannot be overstated,” said Dr. Liu. 

Next Steps

The researchers plan to collaborate with local lung cancer screening programs to incorporate the findings from this study into a pilot program of smoking cessation counseling sessions. 

“We’ve been encouraging people to quit smoking for a long time. These results add more weight to this public health message and provide additional incentive for smokers—particularly those who have smoked for many years—to quit. The improvements in survival seen even with quitting a short time before lung cancer diagnosis show that it’s never too late to stop smoking,” said ASCO President Howard A. “Skip” Burris III, MD, FACP, FASCO.

Disclosures: ILCCO studies have multiple supporters, including Alan Brown Chair in Molecular Genomics, National Cancer Institute grants, the Intramural Research Program of the Center for Cancer Research, Mayo Foundation, etc. For full disclosures of the study authors, visit

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.