Risk of Lung Cancer in Former Smokers

It's significant, but quitting is always worthwhile

The majority of people who develop lung cancer today are non-smokers, not current smokers. Non-smokers include both former smokers and never-smokers (people who have smoked zero to 100 cigarettes in their lifetime).

Lumping these two groups together can be helpful in some respects. But when you unpack the data, it's clear that despite having kicked the habit, former smokers are at a significantly high risk of lung cancer than never-smokers. And the risk remains substantially elevated even 25 years after quitting.

That said, the risk does decrease somewhat with time. And without question, becoming a former smoker is one of the best things you can do to reduce your cancer risk and improve your overall health.

It's never too late to quit and it's always worthwhile.

Lung cancer percentage for smokers
Illustration by Joshua Seong. © Verywell, 2018. 

Lung Cancer Risk After Quitting By Decade

Researchers looked at over 600 people who were referred for lung cancer surgery and who were asked the question, "Did you smoke, and if so, when did you quit?"

Of these patients, 77% had a history of smoking in the past, but only 11% were current smokers. (This is common.) The average patient had quit smoking 18 years before being diagnosed with lung cancer.

The former smokers were broken down further by how long they had been "smoking abstinent:"

  • 14% had been smoke-free for less than a year
  • 27% were smoke-free for one to 10 years
  • 21% were smoke-free for 10 to 20 years
  • 16% were smoke-free for 20 to 30 years
  • 11% were smoke-free for 30 to 40 years
  • 10% were smoke-free for 40 to 50 years

The conclusion was that the majority of patients in this group had been smoke-free for more than a decade prior to their diagnosis of lung cancer.

It is important to note that this group was referred for surgical treatment of lung cancer, and as such, were likely in the earlier stages of the disease.

A Closer Look: Risk Up to 25 Years After Quitting

A larger 2018 study also looked at the risk of lung cancer after quitting smoking in almost 4,000 original participants and more than 5,000 of their children.

Roughly 40% of lung cancer cases occurred in people who had quit smoking more than 15 years before their diagnosis.

More specifically, the risk of developing lung cancer after quitting in former heavy smokers was compared with the risk of lifelong non-smokers from five to 25 plus years after quitting. Here's what they found:

Years After Quitting Heavy Smoking  Risk Compared to Lifelong Non-Smokers
 5  12.12 times greater
 5 to 10  11.77 times greater
10 to 15   7.81 times greater
15 to 25   5.88 times greater
Over 25   3.85 times greater

It's noteworthy (and concerning) that the risk to a former heavy smoker is almost four times higher than a never-smoker even 25 years after quitting. That interval of time is a decade beyond the current recommendations for lung cancer screening (outlined below).

Moreover, a 2019 study found that lung cancer screening may even play a role for never-smokers.

What This Means for Former Smokers

Lung cancer is most treatable in the early stages. When it is discovered early, surgery can offer the chance of a cure.

What does this mean for you personally? What should you do if you quit smoking 10 years ago, 20 years ago, or more?

The answer at the current time depends on how much you smoked and when you quit. If you meet the criteria for screening, this is an excellent option.

If you don't, you may wish to talk to your doctor about lung cancer screening anyway, especially if other risk factors are present.

Get Screened

Screening for lung cancer has the potential to decrease the death rate from the disease by 20% in the United States.

The U.S. Preventive Services Task Force recommends using computerized tomography (CT) to screen for lung cancer in people who:

  • Are between the ages of 50 and 80
  • Have a 20 pack-year history of smoking. (A pack-year is calculated by multiplying the years smoked by the number of packages smoked per day. For example, if you smoked two packs per day for 15 years, that would equal 30 pack-years.)
  • Currently smoke or have quit smoking in the last 15 years
  • Are healthy enough to have surgery if an abnormality is found

Be Aware of Symptoms

Having an awareness of the symptoms of lung cancer could mean the difference between finding your disease early or when it has already spread—even if you also get screened, as these tests don't detect all cancers.

Even so, studies have revealed the majority of people are not familiar with the most common symptoms. Part of this is that lung cancer is changing. The types of lung cancer most common in the past are different than the types most common today.

For example, forms of lung cancer such as squamous cell carcinoma of the lungs and small cell lung cancer have become less common. Those cancers tend to grow near the large airways of the lungs and cause symptoms early on, such as a persistent cough or coughing up blood.

Today, lung adenocarcinoma is the most common type of lung cancer. These cancers tend to grow in the outer regions of the lung, rather than near the airways. Symptoms are often a vague sense of shortness of breath than many people disregard as being due to getting older or due to inactivity.

Know Your Risk Factors

In addition to knowing the symptoms of lung cancer, it's important to be aware of your risk factors. These obviously include smoking, but also family history, occupational exposure to chemicals linked to lung cancer, elevated radon levels in the home, and more.

Mention any that apply to you to your doctor, as it may factor into their care decisions.

Be Your Own Advocate

If you have any symptoms of lung cancer or any symptoms that don't have an obvious cause, talk to your doctor. If you don't get an adequate explanation for your symptoms, ask for further studies or get a second opinion.

It's not only the general public that is surprised when never-smokers and former smokers who quit long ago develop lung cancer. Many physicians are as well, as they may not have lung cancer high on their radar screen when evaluating non-smokers.

Among lung cancer survivors, a frequent complaint is that their symptoms weren't addressed aggressively enough, or were dismissed since they either never smoked or had kicked the habit.

Remember: Anyone who has lungs can get lung cancer.

A Word From Verywell

It can be discouraging to hear about the persistent risk of lung cancer after quitting smoking. It's important to note that the risk does decrease, and unlike lung cancer risk, the risk of heart disease decreases fairly rapidly.

Quitting makes a difference. Even if you do develop lung cancer, know that survival rates are better in former smokers than current ones.

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