A retrospective analysis of National Lung Screening Trial (NLST) exams has shown that most lung cancers that were detected within a year after a negative CT screening exam—some 40 of 44, or 91 percent—were present but overlooked at the screening.

The analysis was published online Jan. 3 in European Radiology.

David Gierada, MD, of Washington University School of Medicine in St. Louis and colleagues reviewed the screening CTs of all 44 NLST participants who were diagnosed with interval lung cancer after an annual negative screening and before the next scheduled scan.  

The researchers matched these cases against a control group of participants who had negative CT screens and did not develop lung cancer.

The team used a majority consensus process to classify each CT screen as positive or negative according to NLST criteria, then estimated the likelihood that any abnormalities detected retrospectively were due to lung cancer.

They found that all the cancer cases had a higher estimated likelihood of lung cancer (P < 0.001) at screening.

Their other key findings:

• Compared with the 40 of 44 cases in the study group that met the NLST criteria for a positive screen, only 17 of 44 controls (39 percent) did so (P < 0.001).  
• Abnormalities included pulmonary nodules of 4 millimeters or larger (n = 16), mediastinal (n = 8) and hilar (n = 6) masses, and bronchial lesions (n = 6).
• Cancers were stage III or IV at diagnosis in 32 of 44 cases (73 percent).
• Some 37 of 44 patients (84 percent) died of lung cancer, compared to 225 of 649 (35 percent) for all screen-detected cancers (P < 0.0001).

The authors do not specify the chronology of the study period in their study abstract.

“Awareness of missed abnormalities and interpretation errors may aid lung cancer identification in CT screening,” Gierada and colleagues conclude. “Awareness of error types may help identify lung cancer sooner.”