Low-dose CT lung cancer screening detects more early cancers in at-risk patients than radiography, but with lower positive predictive value.
Two annual incidence screenings with low-dose CT increases early lung cancers diagnosis and decreases later stage diagnosis, according to a study published in TheNew England Journal of Medicine.
Researchers from the National Lung Screening Trial evaluated the utility of three annual screenings (rounds T0, T1, and T2) with low-dose helical CT compared with chest radiography to assess possible reduction in mortality from lung cancer.
A total of 53,454 participants who were at risk for lung cancer were enrolled into the study between August 2002 and April 2004. The participants were randomly assigned to screenings by either low-dose CT or radiography, performed from August 2002 through September 2007. Follow-up continued through to December 2009. The images were reviewed by individual radiologists.
The study’s primary end point was lung cancer-specific mortality. The researchers evaluated the rate of participant adherence to the screening protocol, screening and downstream diagnostic test results, features of the lung-cancer cases, and first-line treatments.
The results showed that T1 and T2 rounds had positive screening results in 27.9 percent and 16.8 percent of participants in the low-dose CT group and in 6.2 percent and 5.0 percent in the radiography group, respectively.
At T1, the sensitivity was 94.4 percent in the low-dose CT group, the specificity was 72.6 percent, the positive predictive value was 2.4 percent, and the negative predictive value was 99.9 percent. At T2, the positive predictive value increased to 5.2 percent. In the radiography group, the sensitivity was 59.6 percent, the specificity was 94.1 percent, the positive predictive value was 4.4 percent, and the negative predictive value was 99.8 percent at T1; both the sensitivity and the positive predictive value increased at T2.
Among lung cancers of known stage at T1 in the low-dose CT group, 87 (47.5 percent) were stage IA and 57 (31.1 percent) were stage III or IV. In the radiography group, 31 (23.5 percent) were stage IA, and 78 (59.1 percent) were stage III or IV at T1. These differences in stage distribution between groups persisted at T2.
At the T1 screening, the clinical or pathological stage was known in 183 of 186 participants in the low-dose CT group and 132 of 133 participants in the radiography group. Of these, 47.5 percent had stage 1A cancer, 21.3 percent had stage IB, IIA, or IIB, and 31.1 percent had stage III or IV. Among those in the radiography group, 23.5 percent were diagnosed with stage IA cancer, 17.4 percent with stage IB, IIA, or IIB, and 59.1 percent with stage III or IV. Stage distributions at T2 were similar to those at T1 in each group.
The researchers noted that the increase in early-stage lung cancers was associated with a decrease in late-stage lung cancers among those in the low-dose CT group. Only 138 stage IV cases per 100,000 person-years were detected compared with 204 in the radiography group.
The researchers concluded that low-dose CT did detect more early-stage lung cancers when compared with radiography, but with a lower measured positive predictive value.