Previous Smoking Cessation Improves Survival Odds of Lung Cancer

A new Harvard study suggests that people who quit smoking before their lung cancer diagnosis have significantly better odds of survival. Compared with those who never smoked, current smokers who were being treated for non-small-cell lung cancer (NSCLC) had 68 percent higher mortality and former smokers had 26 percent higher mortality.

The longer a patient had gone without smoking before their lung cancer diagnosis, the more improved their odds of survival were, according to the findings, which were published today in JAMA Network Open.

These findings show that for smokers, it’s critical to stop smoking as soon as possible, says the senior author, David Christiani, MD, MPH, a professor of environmental genetics at the Harvard T.H. Chan School of Public Health in Boston. “For former smokers, it is important to remain ‘former,’ and the longer one is away from smoking, the better the outcome of lung cancer treatment should you develop the disease,” Dr. Christiani says.

How Many People Are Affected by Lung Cancer?

Lung cancer is the second most common cancer in both men and women, according to the American Cancer Society. In 2023, it’s estimated that there will be nearly 240,000 new cases of lung cancer in the United States, and about 125,000 deaths from lung cancer. In general, 80 to 85 percent of those are non-small-cell lung cancer (NSCLC).

To find out more about the effect of quitting smoking before NSCLC diagnosis, researchers looked at more than 5,594 people enrolled in the Boston Lung Cancer Survival Cohort at Massachusetts General Hospital between 1992 and 2022.

Of these participants, 795 had never smoked, 3,308 were former smokers, and 1,491 were current smokers. Subjects completed questionnaires about their smoking habits and other health and demographic information at baseline, with the researchers checking in on their survival every 12 to 18 months.

Doubling the Years of Smoking Cessation Prediagnosis Was Significantly Associated With Prolonged Survival

The study is unique in that it examined mortality not just among current and never-smokers, but also among former smokers. The findings are further strengthened because of the range of the participants’ smoking histories, with some having stopped smoking a few years before their diagnosis and others having stopped for several decades, according to the authors.

During the study period, 3,842 of the participants died: 79.3 percent of the current smokers, 66.8 percent of the former smokers, and 59.6 percent of the never smokers.

Key findings included:

Never smoking was associated with the best odds of survival after a lung cancer diagnosis; but the findings showed significant associations between lower mortality and having quit smoking prediagnosis.
The longer a patient had gone without smoking, the more health benefits they accumulated. In former smokers, doubling the years of smoking cessation before their lung cancer diagnosis was significantly associated with prolonged survival.
A doubling of smoking pack years was associated with shorter survival among current and former smokers.

“These results are consistent with the 2020 Surgeon General’s Report (SGR) demonstrating that quitting smoking even after a cancer diagnosis is associated with improved cancer treatment outcomes,” says Christiani.

The new findings suggest that the benefit of prediagnosis smoking cessation persists even after lung cancer is diagnosed, and that long-term quitters have a better response to treatments such as surgery, radiation, and chemotherapy, he says. “For those with curative treatment, the chances of remaining disease-free are much better, and, in more advanced disease, the chances of longer survival are better,” says Christiani.

This is a large, well-designed study that confirms that quitting smoking before your lung cancer diagnosis is better — former smokers tend to live longer than smokers, says Peter Shields, MD, a medical oncologist and the Julius F. Stone Chair in Cancer Research at the Ohio State University Comprehensive Cancer Center in Columbus. Dr. Shields was not involved in this study.

Does Quitting at the Time of Lung Cancer Diagnosis Prolong Survival?

“The question that this study doesn’t address is the million-dollar question: Does quitting smoking at the time of lung cancer diagnosis improve your outcome and help you live longer?” says Shields. “We have these patients who come in with lung cancer, and we tell them to stop smoking because we know that it reduces toxicity. But it would be nice if we actually knew that it also helped them live longer.”

That’s a critical research gap, but if the researchers continue to follow these people, they could have that data in the future, he adds.

Cessation at Any Age Has Value

Quitting smoking is always a good idea. This study just reinforces that message: Even before you’re diagnosed with lung cancer, no matter how old you are, you should quit smoking, because you’ll have better survival, says Shields.

“What’s a shame is that people who quit smoking still get lung cancer. There are some people who wrongly think that if you quit smoking for 10 or more years, that your risk goes down to the lung cancer risk for never-smokers. That’s not true,” he says.

People who quit smoking cut their risk of lung cancer by 30 to 50 percent after 10 years compared with people who keep smoking, and they cut their risk of cancer of the mouth or esophagus in half within 5 years of quitting, according to the National Cancer Institute.

Shields says it would have been interesting if this study had included the data broken down by type of lung cancer, mutation status, and treatment, because those factors may influence survival rates as well.

The researchers noted that associations between survival and smoking history may vary depending on the clinical stage at which lung cancer was diagnosed, and that the study did not account for the different kinds of treatment participants were receiving.

Ready to Quit Smoking?

If you’re ready to stop smoking, the CDC website offers resources to get you started. In addition to counseling and support groups, there are also many medications your doctor can prescribe that can more than double your chances of successfully kicking the habit, according to the agency.