AIM: Lung cancer CT screening can yield high false-positive rates
Researchers from the National Institutes of Health, National Cancer Institute in Bethesda, Md., sought to quantify the cumulative risk facing an individual participating in a one- or two-year lung cancer screening exam, based on at least one false-positive finding. In addition to determining the rates of false-positive findings, lead author Jennifer M. Croswell, MD, and colleagues identified rates of unnecessary diagnostic procedures that are potentially brought on by these false-positive findings.
The authors wrote, “direct-to-consumer promotion of lung cancer screening has increased, especially low-dose CT. However, screening exposes healthy persons to potential harms, and cumulative false-positive rates for low-dose CT have never been formally reported.”
The randomized, controlled two-year study conducted in six centers of low-dose CT--which the researchers compared to chest radiography--recruited a cohort of 3,318 current or former smokers who had quit in the past 10 years between the ages of 55-74 from the ongoing National Lung Screening Trial, all of whom had a smoking history of 30 pack-years or more and no history of lung cancer.
The researchers randomly assigned the participants to low-dose CT or chest radiography with baseline and one repeated annual screening, and follow-up was conducted at one year after the final screening. Assignment was concentrated and stratified by age, sex and study center.
Croswell and colleagues took note of any false-positive screenings, defined as a positive screening with a completed negative work up or 12 months or more of follow up with no lung cancer diagnosis.
By way of a Kaplan-Meier analysis, the researchers determined that an individual’s cumulative probability of one or more false-positive finding from low-dose CT examinations was 21 percent after one screening and 33 percent following the second exam. The false-positive rates for chest radiography however following the first exam were 9 percent and 15 percent after the second screening.
In addition, the authors wrote that “more than half of participants with false-positive chest radiography or CT had at least one additional imaging exam—some at higher radiation doses than that of the original test—which exposed these persons to a theoretical risk for radiation-induced carcinogenesis.”
Moreover, they found that a total of 7 percent of participants with a false-positive low-dose CT exam and 4 percent with a false-positive chest radiography result underwent a resulting invasive procedure.
Noting that the study was limited to two rounds of exams and follow-up after the second screening was limited to 12 months, the researchers said that the false-negative rate is most likely underestimated and that further study of resulting economic, psychosocial and physical burdens of these methods is necessary.