Initial LDCT appearance of incident lung cancers in the ITALUNG trial

• 85% of screen-detected incident lung cancers show focal abnormalities in prior LDCTs.
• These tumors can initially show a non-nodular shape.
• Persistent focal pulmonary abnormalities need to be monitored in screening LDCTs.

ObjectivesTo characterize early features of lung cancers detected with low-dose computed tomography (LDCT) screening.Materials and methodsTwo radiologists reviewed prior LDCTs in 20 incident cancers diagnosed at annual repeat screening rounds and 83 benign nodules observed in the ITALUNG trial.ResultsNo abnormality was observed in 3 cancers. Focal abnormalities in prior LDCT were identified in 17(85%) cancers (14 adenocarcinomas; 14 stage I). Initial abnormalities were intra-pulmonary in 10, subpleural in 4 and perifissural in 3. Average mean diameter was 9 mm (range 4.5–18 mm). Nine exhibited solid, 4 part-solid and 4 non-solid density. The margins were smooth and regular in 5 cases, lobulated in 6, irregular with spiculations in 3 and blurred in 3. Ten (59%) initial focal abnormalities had a round or oval nodular shape, but 7(41%) had a non-nodular complex (n = 5) or “stripe-like” (n = 2) shape. Bronchus sign was observed in 3 cases and association with cystic airspace in 2 cases. Non-solid density, complex or “stripe-like” shape, bronchus sign and association with cystic airspace had a specificity higher than 90%, but positive predictive value of every feature of incident lung cancers was low (range 10.4–50%).ConclusionsThe vast majority of cancers diagnosed at annual repeat show corresponding focal lung abnormalities in prior LDCTs. Perifissural location and non-nodular shape do not exclude the possibility of early lung cancer. Since specificity of the early features of incident lung cancer is incomplete and their positive predictive value is low, all focal pulmonary abnormalities detected in screened subjects should be re-evaluated in subsequent LDCTs.