Smoking cessation improves lung cancer survival

Quitting smoking as recently as 2 years prior to lung cancer diagnosis may improve survival, according to a study from ASCO20.

“Individuals who quit smoking showed consistently higher survival rates among lung cancer patients, including those who quit within 2 years of their diagnosis, independent of other known prognostic factors,” said study lead author Dr Aline Fusco Fares from the Princess Margaret Cancer Centre in Toronto, Ontario, Canada, and co-authors.

Fares and co-authors used individual data from 17 studies in the International Lung Cancer Consortium (ILCCO) database. Included in the study were 35,428 patients with lung cancer (median age 66 years, 52 percent male, 78 percent Caucasian), of whom 47.5 percent were current smokers, 30 percent were former smokers, and 22.5 percent were never smokers at time of diagnosis.

Compared with current smokers, overall survival (OS) after lung cancer diagnosis was significantly improved in former smokers (adjusted hazard ratio [adjHR], 0.88, 95 percent confidence interval [CI], 0.86–0.91) and never smokers (adjHR, 0.76, 95 percent CI, 0.73–0.8; p<0.001 for both). [ASCO20, abstract 1512]

Among former smokers, OS was improved regardless of time since smoking cessation (TSSC) with a 12, 16, and 20 percent improvement with <2 years, 2–5 years, and >5 years since smoking cessation compared with current smokers (adjHR, 0.88, 95 percent CI, 0.82–0.94, adjHR, 0.84, 95 percent CI, 0.77–0.9, and adjHR, 0.8, 95 percent CI, 0.76–0.84, respectively; p<0.001 for all).

“When looking only at current and former smokers, we found that there is a stepwise advantage to quit smoking; even for those quitting within 2 years prior to lung cancer diagnosis, there is a significant survival benefit,” said the authors.

The findings were also generally consistent regardless of whether patients smoked less or more than 30 pack-years (eg, adjHR, 0.84 and 0.78 for >5 years since smoking cessation in patients with <30 or >30 pack-years, respectively; p<0.001 for both compared with current smokers).

“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 senior author Dr Geoffrey Liu, also from the Princess Margaret Cancer Centre.

“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,” he added.

Illustrating this was the result of a subgroup analysis of 10,514 patients with cause of death information available. In this group, lung cancer specific survival (LCSS) was greater among patients who had quit smoking, with a significant 15 percent survival benefit among those who had quit >5 years pre-diagnosis compared with current smokers (adjHR, 0.85, 95 percent CI, 0.78–0.92). There was also a nonsignificant trend toward improved LCSS with shorter TSSC (adjHR, 0.93 and 0.95 for 2–5 and <2 years TSSC, respectively).

“Tobacco smoking profoundly impacts lung cancer risk; however, data are limited as to what extent smoking cessation prior to diagnosis impacts lung cancer OS and LCSS,” said the authors.

“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 Fares. “The study’s message is simple: quit smoking now.”