Lung Cancer Risk Drops Almost 40% Within 5 Years of Quitting Smoking

MedicalResearch.com Interview with:
Hilary Tindle, MD, MPH

“Used Cigarette Butts” by Indi Samarajiva is licensed under CC BY 2.0Associate Professor of Medicine and theWilliam Anderson Spickard, Jr., MD Chair in Medicine
Founding Director of ViTAL, the Vanderbilt Center for Tobacco, Addiction and Lifestyle
Division of Internal Medicine & Public Health and Vanderbilt Ingram Cancer Center (VICC)

MedicalResearch.com: What is the background for this study?

Response: Lung cancer is the most common cause of cancer related death for men and women ,and cigarette smoking is responsible for almost 9 of our every 10 lung cancers in the US. Lung cancer screening can reduce the risk of death from lung cancer by about 20% or even higher if screening is combined with quitting smoking.

We know that lung cancer risk is lower in people who quit smoking, compared to those who continue to smoke, but it was not clear how quickly this risk drops after quitting. Most prior studies on this subject assessed smoking status (current, former, never) at relatively few timepoints. By asking about smoking more frequently (every couple of years), we can get a better picture of a person’s true exposure to cigarette smoke and take into account periods where someone may have smoked more, less, or even quit altogether. Some people may start and stop multiple times over their lifetime.

Another question was exactly how long the risk of lung cancer stays elevated after quitting smoking. Again, by asking about smoking multiple times over someone’s lifetime, we get a better picture of how long they were truly smoke free.

MedicalResearch.com: What are the main findings?

  •  We analyzed data from the Framingham Heart Study Original and Offspring cohorts (almost 9000 people total) to study the risk of lung cancer after quitting smoking, and to determine if the risk of lung cancer ever goes back to that of someone who has never smoked (termed a “never smoker”). Study participants were followed for a median of almost 30 years, and were asked about smoking every 2-4 years.
  • We focused on heavier smokers, who had smoked more than 21 pack-years. (A “pack-year” is a way to quantify how much someone has been exposed to cigarette smoke. Pack years are the product of years of smoking times the amount smoked. For example, someone who smoked 1 pack of cigarettes per day for 20 years would have 20 pack years. Another person who smoked 2 packs per day for 10 years would also have 20 pack years.) As expected, the risks of lung cancer were highest among current smokers, followed by former smokers, followed by never smokers.
  • Compared to never smokers, former smokers had higher lung cancer risk: about 12 times higher within 10 years since quitting (YSQ), about 7 times higher from 10-15 YSQ, about 6 times higher from 15-25 YSQ, and over 3 times higher even after 25 YSQ.
  • Compared to current smokers, former smokers had lower lung cancer risk: 39% lower within 5 YSQ, which continued to drop over time.
  • Among all former smokers, about 4 in 10 lung cancers occurred after more than 15 YSQ, which is beyond the window of eligibility for current screening guidelines.

In the future, after additional study, guidelines may decide to extend the window of lung cancer screening beyond 15 YSQ. However, additional modeling studies are likely needed before making that determination. For now, anyone who qualifies for lung cancer screening based on age, pack years, and years since quitting, should have it.

MedicalResearch.com: What should readers take away from your report?

Response: If you currently smoke cigarettes, now is a great time to quit. The results of this study show that lung cancer risk drops almost 40% within 5 years since quitting, compared to people who continue to smoke.

If you already quit smoking, congratulations on taking that major step.

Whether you currently smoke, or if you quit smoking within the last 15 years, talk to your doctor to see if you are eligible for lung cancer screening. 

MedicalResearch.com: What recommendations do you have for future research as a result of this work?

 Response: We would like to see additional research from different groups to determine if the current lung cancer screening guidelines should potentially be altered to include those who quit more than 15 years ago. Again, this is a decision may require additional study, including an understanding of why some former smokers remain at elevated risk of lung cancer. Perhaps studying genetic variation could shed some light on this question.  

MedicalResearch.com: Is there anything else you would like to add?

Response: Yes, we would like to thank the NIH and particularly the NHLBI for supporting the Framingham Heart Study (FHS) and studies like it, and also to all the participants in the FHS for giving their information for decades, to the benefit of all Americans and the world. We consider studies such as the FHS to be “national treasures” in that they provide critical information for doctors and researchers to improve healthcare. The FHS is most often thought of as a cardiovascular dataset, but it also captures information on cancer. In the case of the current study, we re-analyzed information that was already collected, which is one of the efficient and low cost methods of conducting research. 

Citation:

 Hilary A Tindle, Meredith Stevenson Duncan, Robert A Greevy, Ramachandran S Vasan, Suman Kundu, Pierre P Massion, Matthew S Freiberg. Lifetime Smoking History and Risk of Lung Cancer: Results From the Framingham Heart Study. JNCI: Journal of the National Cancer Institute, 2018; DOI: 10.1093/jnci/djy041

 

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