Screening for Lung Cancer with Low-Dose CT Scan

Lung cancer is by far the most deadly type of cancer in the United States. Over 150,000 men and women die from lung cancer per year, easily making it the leading cause of cancer death in the country.¹ There are over 210,000 newly diagnosed cases of lung cancer in the United States each year.¹ Rates of lung cancer have been decreasing recently due to a decline in smoking, but it is obviously still a major public health problem. In 2013, the United States Preventive Services Task Force (USPSTF) published recommendations for lung cancer screening, which will be the focus of this article.

First, let’s talk about the risk factors for lung cancer. By far, the most significant risk is smoking. Smoking is responsible for 80% to 90% of all lung cancers.² Secondhand exposure to tobacco smoke is another big risk factor, and the younger the age of exposure, the higher the risk of developing lung cancer. Smaller, less important risk factors include exposure to environmental toxins such as radon, asbestos, air pollution, and others. History of radiation treatments to the chest also increases the risk, as does increasing age and family history of lung cancer.² Just under 1 in 5 Americans currently smoke, and there are many more who have smoked in the past… so unfortunately lung cancer isn’t going away anytime soon. 

The test that is used to screen for lung cancer is a low-dose CT (computed tomography or “CAT scan”) of the chest. This is a newer form of CT scan that is very fast, and rotates in a spiraling motion taking several mages of the lung fields. As the name suggests, it uses a smaller dose of radiation than a traditional CT. 

First, here’s the good news: screening a specific high-risk population on an annual basis with this test has led to up to a 20% decrease in mortality from lung cancer.³ That’s pretty good! The official “number needed to screen”, which once again is the number of screenings needed to take place in order to save one life from the cancer, is 312.⁴ Once again, that’s not insignificant.

Now here’s the bad news: there are a lot of false positives. When you have this test done, you have a 20% to 50% chance of having a positive result.^3,5 Of the positive results upon initial screening, about 95% of those aren’t actually going to be cancer.⁵ It is hard to tell if suspicious masses found on screening CTs are actually cancer, or a benign nodule such as a granuloma. As you can imagine, any positive test leads to increased anxiety and stress, repeat imaging (which means more radiation), and in some cases actually undergoing invasive diagnostic procedures which carry their own risks.

Regardless, the USPSTF and many other American medical societies have recommended this screening for a specific high-risk population. According to the USPSTF, there are three criteria that make a person a candidate for this screening test.

1. Age between 55 and 80*.
2. A “pack-year history” that is greater than 30. A “pack-year” is a simple calculation where you multiply the number of years that you’ve smoked by the average number of packs of cigarettes per day during that time period. So, for example, if I have smoked two packs a day for 17 years, my pack year history is 34.
3. The individual must be currently smoking or has quit within the past 15 years, or less than 15 years ago.⁶ 

                                                                                 ^{* American Cancer Society recommends cutting off screening at age 75.}

You can view the USPSTF recommendation here. 

To review; benefits versus risk: 

The benefits are clear, up to a 20% reduction in death from lung cancer and a 6.7% reduction in all-cause mortality in the individuals that are screened. This gives a number needed to screen (NNS) of 312 to save 1 person’s life.

The risks include a high false-positive rate, which leads to more follow-up, causes anxiety, more radiation exposure, and possibly invasive testing.

As usual, a strategy even better than screening would be prevention. If you’re not a smoker, don’t start. If you are a smoker, you ought to quit. Also, avoid exposure to secondhand smoke and other environmental pollutants as much as possible. 

If you would like information about smoking cessation including strategies and tips to successfully quit, read the article or watch the video here in the Health Confidence Academy's library. 

If you meet the “high-risk” criteria, undergoing screening is definitely something to consider and talk about with your doctor. Just remember that there’s a very high chance that you’re going to have a positive result, and about 19 times out of 20 the positive result won’t actually be cancer. 

Please share this article with someone that you know and love; you may save a life!

References

1. U.S. Cancer Statistics Working Group. United States Cancer Statistics: 1999–2014 Incidence and Mortality Web-based Report. Atlanta, GA. Department of Health and Human Services, Centers for Disease Control and Prevention, and National Cancer Institute; 2017.
2. Center for Disease Control and Prevention. What are the risk factors for lung cancer? https://www.cdc.gov/cancer/lung/basic_info/risk_factors.htm. Most recent update May 31, 2017. Accessed April 14, 2018.
3. Linda L. Humphrey, MD, MPH; Mark Deffebach, MD; Miranda Pappas, MA; Christina Baumann, MD, MPH; Kathryn Artis, MD, MPH; Jennifer Priest Mitchell, BA; Bernadette Zakher, MBBS; Rongwei Fu, PhD; and Christopher G. Slatore, MD, MS. Screening for Lung Cancer With Low-Dose Computed Tomography: A Systematic Review to Update the U.S. Preventive Services Task Force Recommendation. Annals of Internal Medicine. July 30, 2013.
4. Kelly M. Latimer, MD, MPH, Timothy F. Mott, MD. Lung Cancer: Diagnosis, Treatment Principles, and Screening. American Family Physician. February 15, 2015. 
5. Allen F. Shaughnessy, PharmD. High False-Positive Rate with Lung Cancer Screening. American Family Physician.July 15, 2017. 
6. Final Recommendation Statement: Lung Cancer Screening. U.S. Preventive Services Task Force. December 2013. www.uspreventiveservicestaskforce.org