P1.11-06 Lung Cancer Probability in New Perifissural Nodules Detected in a Lung Cancer Screening Study

In incidence lung cancer screening rounds, new lung nodules are a regular finding, with a higher lung cancer probability than baseline nodules. A substantial number of screen-detected nodules is classified as perifissural nodule (PFN). Previous studies showed that baseline PFNs and PFNs in clinical settings represent non-malignant lesions such as intrapulmonary lymph nodes. Whether this is also the case for incident PFNs is unknown. This study evaluates all newly detected nodules in the Dutch-Belgian randomized-controlled NELSON study with respect to perifissural classification and lung cancer probability. All NELSON participants with a new solid nodule detected in screening round 2, 3 or 4 (1, 3, and 5.5 years after baseline, respectively), were enrolled in this substudy. Nodules were classified into three groups: intraparenchymal, vessel attached or fissure attached. Screening CT scans of participants with lung cancer based on a nodule classified as fissure attached, were re-evaluated by two radiologists (4 and 6 years of experience) to check whether this nodule was a typical, atypical or non-PFN. The fissure-attached cancers were matched based on size with benign cases (1:4), and the radiologists were blinded for the final nodule outcome. In case of discrepancy, a third radiologist (13 years of experience) arbitered. 1,484 new nodules were detected in the second, third and final NELSON screening round in 949 participants (77.4% male, median age 59 [interquartile range: 55-63]). 1,393 nodules (93.8%) were benign based on 2 year follow-up or pathology; 96 of these (6.9%) were fissure attached. Lung cancer diagnosis was made in 74 new nodules in 74 participants (7.8% of participants with a new nodule). Nine lung cancers (12.1%) were fissure attached and re-evaluated by the radiologists. None of the fissure attached malignant new nodules was classified as a typical or atypical PFN. None of the lung cancers that originated from a new nodule in the NELSON study was classified as a typical or atypical PFN. Our results suggest that also in the case of a new PFN, it is highly unlikely that these PFNs will be diagnosed as lung cancer.