By Diana Zuckerman, PhD
Lung cancer has a poor prognosis, with a survival rate of 20% at 5 years, but early-stage lung cancer has a better survival rate and is more responsive to treatment. Medicare and U.S. insurance companies now pay for lung cancer screening with low-dose CT (LDCT) scans for former smokers to help diagnose lung cancer at its earliest stages. Still, screening has not been shown to reduce most lung cancer deaths.
Three major studies were used to inform the latest lung cancer screening guidelines proposed by the US Preventative Services Task Force: The National Lung Cancer Screening Trial (NLST), Nederlands-Leuvens Longkanker Screenings Onderzoek (NELSON) trial, and Cancer Intervention and Surveillance Modeling Network (CISNET). It is important to note, these studies differed in eligibility criteria (age and smoking history), number of screening rounds (2-5), screening intervals (annual, biannual, escalating), and definitions of a positive screen (4mm, 5mm, volume-based) making it difficult to uniformly apply results to the clinical setting.
Still, these studies found fewer deaths in patients 50-80 years of age who had smoked for at least 20 pack-years (1 pack of cigarettes per day for 20 years, or 2 packs a day for 10 years, etc.) within the past 15 years and were screened with LDCT scans rather than chest x-ray. Patients were 20% less likely to have died within 6.5 years of screening and 25% less likely to have died within 10 years. Lung cancer was also more frequently diagnosed at an early-stage rather than at a late-stage, yielding the best chance for treatment success and survival.
However, the populations in these studies were not reflective of a diverse patient population and the majority were white, male, affluent, and did not have any other major diseases. This means that there is a major potential for discrepancies in screening effectiveness across a more diverse patient population and a sicker population, which is more reflective of the clinical setting. Screening can also lead to serious harms including false-positive results (a result showing that you have lung cancer when you do not), incidental findings that lead to invasive testing, and increased radiation exposure.
Overall, major questions regarding lung cancer screening still remain:
- What evidence is there that Medicare patients with a 20-pack-year smoking history benefit from LDCT screening?
- Are these patients healthy enough to benefit from surgery?
- What are the harms of lung cancer screening and finding incidental health abnormalities?
The US Preventive Services Task Force has recommended LDCT screening for people ages 50-80 with a 20 pack-year history of smoking within the last 15 years. However, those experts warn that “screening does not prevent most lung cancer deaths.” In fact, even if patients who are screened with LDCT scans are diagnosed earlier and live longer with the diagnosis, they may die at the same age they would have without screening. In other words, a patient diagnosed after screening at age 65 might live to be 68 whereas, if they were not screened, they might have been diagnosed at 67 but still have died at the age of 68. Age is also an important risk factor for lung cancer, and screening Medicare patients may decrease the number of lung cancer deaths by intervening on the highest-risk population. However, surgical recovery is more taxing and there are fewer quality years to be gained within this population.
The answer to the second question is difficult to know. The patients studied in the major clinical trials used by the US Preventative Services Task Force to make their recommendation on lung cancer screening did not have any other major diseases apart from lung cancer. It is also recommended that screening be discontinued if a patient develops a significant health problem. In one particular study, the NLST, half were as likely to have emphysema, diabetes, or heart disease as most smokers the same age. Typical Medicare patients eligible for LDCT screening generally have more health problems. It is less likely that Medicare patients would be healthy enough to undergo medical or surgical cancer treatment and fewer than 7% would likely benefit by living longer.
Another major concern is that lung cancer screening has health risks. A range of false-positive (a result showing that you have lung cancer when you do not) rates have been reported from 10-29% at initial screening. Aside from the unnecessary anxiety a false-positive result can cause, it can also lead to unnecessary radiation exposure from repeat CT scans, unnecessary procedures such as biopsies, and in extreme cases unnecessary surgery occurring in 0.5-2% of the study population who underwent LDCT screening. Lung cancer screening can also detect more than just lung cancer and other significant abnormalities may be found, termed incidental findings. Incidental findings have been reported at a rate of 10-34% with 89% of incidental findings requiring further clinical evaluation. While this may present an opportunity for early intervention on an important condition that otherwise would not have been found. Incidental findings may also cause unnecessary financial and emotional burdens, result in harmful complications, or lead to inappropriate medical care.
The benefits and risks of lung cancer screening with LDCT scans will likely continue to evolve. Currently, there are major gaps in lung cancer screening research that need to be addressed in order to fully understand the impact of the US Preventative Services Task Force recommendations: (1) the impact of lung cancer screening on mortality across age, health status, and smoking history, (2) effectiveness in a more diverse patient population, and (3) the long-term, cumulative harms of low-dose radiation exposure.
Last updated July, 2023