​​​​Drs. Wei Xu, (L), and Geoffrey Liu of Princess Margaret Cancer Centre led the recent study investigating the duration of smoking cessation and lung cancer patient survival. (Photos: UHN)

It is well-known that smoking is the number one risk factor for lung cancer, but it's hard for smokers to kick the habit.

New research from UHN has found that, by the time of diagnosis, lung cancer patients who managed to stop smoking for as short a time period as one year can live longer than those who still smoked at the time of diagnosis.

"Before this study, we could not give a concrete recommendation to current smokers on the benefits of quitting," says Dr. Geoffrey Liu, Senior Scientist who leads the research program for lung cancer screening at Princess Margaret Cancer Centre. “Now we can say that if one stops smoking, even if they develop lung cancer in the future, they can still enjoy a longer life than those who do not.

"And it doesn't take a decade to see this effect, quitting for as little as one year can already make a difference for improving overall cancer survival."

The study, led by Dr. Liu and Dr. Wei Xu, also of Princess Margaret Cancer Centre, was published in Lancet Public Health.

According to the Canadian Cancer Society, lung cancer is still expected to be the most commonly diagnosed cancer in Canada in 2023 despite efforts to reduce tobacco use.

The study led by researchers at the Princess Margaret came just in time for Lung Cancer Awareness Month, to help smokers take actions and survive a longer life from potential lung cancer.

The significance of the study speaks directly to the fatalism often present in smokers. Since they are already at a higher risk for developing cancer, many individuals continue smoking as they don't believe it will make much of a difference if they stop.

There is also a misconception that it will take many years of willpower to produce any positive impact.

Study tracked more than 40,000 lung cancer patients around the world

At the Princess Margaret Lung Clinic, where heavy smokers are recommended to undergo annual screening for lung cancer, some smokers may take negative screening results as a green light to keep living the way they do, and do not come back after their first screening.

"We needed a more concrete and definitive message to motivate people to quit smoking," says Dr. Liu. "From this study, we can say that if you quit today, you can still live longer if you are diagnosed with lung cancer in your next year's screening."

To investigate how smoking cessation before diagnosis plays a role in cancer survivorship, researchers pooled data from 26 cohort studies in the International Lung Cancer Consortium. These studies tracked 42,087 lung cancer patients across the globe from diagnosis to the date of their last follow-up, or death.

By analyzing their self-reported smoking history at the time of lung cancer diagnosis, the research team divided these patients into three major groups: those who never smoked, current smokers who had smoked within one year of diagnosis, and former smokers who had quit smoking for at least one year before their diagnosis. For the last group, they also looked at various durations of smoking cessation and the relationship to survival.

"The major result we got from this study is that the median survival time – an indicator of how long one can live – improves by eight​ per cent to 15 per cent for former smokers, compared to current smokers at the time of diagnosis.

"The duration of smoking cessation is a key factor impacting how much this improvement can be," says Dr. Wei Xu, corresponding author of the study, a principal biostatistician and clinician scientist at Princess Margaret Cancer Centre and a professor in the Department of Biostatistics at University of Toronto's Dalla Lana School of Public Health.

The study also analyzed possibility of death from lung cancer five years and 10 years after diagnosis.

"Out of 100 patients, if they chose to quit smoking early, three more patients would have been alive at the five-year mark and four more patients would have been alive at the 10-year mark," says Dr. Liu.

"Another noteworthy point is that the study is generalizable," says Dr. Xu. "We have conducted extensive subgroup analyses on different ages, genders, ethnical groups, and stages of cancer.

"The results are consistent."

Dr. Liu adds: "We're able to conclude that benefits of stopping smoking is generally present across all ages, all genders, and different ethnic groups.

"It doesn't matter if you smoked more or less or what stage of lung cancer you end up developing, you will benefit if you quit today."

International research collaboration in lung cancer

Previously, there were several small studies that tried to assess the association between smoking cessation and lung cancer survivorship. However, they were not able to give significant evidence due to their limited sample size.

The current study relied on international research collaboration through the International Lung Cancer Consortium, which provided a large data set for the researchers to draw a definitive conclusion. The consortium was originally established to look at strategies for lung cancer risks and prevention.

Drs. Xu and Liu were able to build research objectives within the consortium that focus on outcomes and survival. By bringing international groups together and compiling all the outcome and survival data, this initiative gives an opportunity for researching different aspects that can impact lung cancer survival beyond smoking cessation.

The current publication is the sixth article since this effort began in 2017. And the Princess Margaret is the host centre for this effort.

"We're looking at all the different factors that might influence lung cancer survival, using an extremely large data set with tens of thousands of individuals from around the world," says Dr. Liu.

"This is by far the largest global consortium in lung cancer."

This work was supported by the Alan B Brown Chair, the Posluns Family Fund, the Lusi Wong Fund, and The Princess Margaret Cancer Foundation.

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