Cancer Trends Progress Report

Percentage of adults at risk for lung cancer due to smoking, aged 55-80 years, who had a CT scan to check for lung cancer within the past year, by sex, race/ethnicity, income, education level, age, and smoking pack years.

Measurement challenges

We track lung cancer screening rates in U.S. adults using a large, national, in-person survey in which people are asked about their health behaviors and the medical care they receive (see Data Source, below). There are important limitations to this method that impact what information we can accurately collect and how confident we can be in the findings. Studies have found that certain types of healthcare survey questions can be difficult for people to clearly understand and answer, and it is easy for some questions to be misinterpreted.

National guidelines state that only individuals with extensive cigarette smoking experience be screened for lung cancer, and this report strives to only include eligible individuals in our measures. One challenge we face is calculation of an accurate measure of lifetime smoking, which is needed to determine whether someone is eligible for screening. Cigarette smoking behaviors can vary from day to day and year to year, yet our survey does not capture such time-specific information; instead, we collect information about average lifetime smoking. In addition, it can be difficult for an individual to accurately recall how many cigarettes he or she smoked a day in years past. Furthermore, an individual may underreport amount smoked given the stigma associated with the activity.

In the case of lung cancer screening, it can be challenging to determine by self-report alone if an individual received an LDCT for the purposes of looking for asymptomatic, previously undetected cancer or precancers (i.e., for screening purposes), or to follow up on symptoms or suspicious findings from a prior test (i.e., for diagnostic purposes). Patients may not know the difference between a screening LDCT and a diagnostic LDCT. Therefore, we ask individuals whether they received an exam to check for lung cancer, and our measures include both screening and diagnostic LDCTs. Though people may have reported LDCT exams that occurred for surveillance following lung cancer diagnosis and treatment, as of 2021 we exclude individuals previously diagnosed with lung cancer, thus minimizing inclusion of surveillance exams. We also exclude individuals who report having an exam to check for lung cancer but then report that they had no exams in the last three years.

The challenges noted above can lead to the overreporting and underreporting of smoking and lung cancer screening; therefore, it is difficult to know whether our measures of lung cancer screening in eligible individuals are overestimates or underestimates. We do not believe that errors are extensive, and as such, we feel that our measures provide good estimates of the true magnitude of lung cancer screening. Furthermore, these data are widely considered to be the best national data on lung cancer screening and are used frequently to track lung cancer screening rates in the U.S.

In addition to the challenges noted above, lung cancer screening is somewhat unique among cancer screening modalities because it does not apply to everyone in a specified age range, but rather only current or former heavy smokers in the age range. This means that the denominator of eligible individuals is considerably smaller than that for other screening modalities. Thus the resultant estimates from NHIS of those screened among the eligible population will have considerably larger standard errors (especially relative to the size of the estimates) than for other cancer sites, and should be interpreted with caution.