Spread Through Air Spaces: Interresponder Agreement and Comparison Between Pulmonary and General Pathologists

Spread through air spaces (STAS), an important prognostic indicator included in the 2015 World Health Organization classification, is defined as micropapillary, solid, and/or single tumor cell clusters beyond the edge of the main mass and distinct from processing artifacts. This study aimed to assess the interresponder agreement on current STAS criteria vs artifacts, identify discrepancies, and compare responses between pulmonary and general pathologists. A multiple-choice online questionnaire illustrating multiple criteria for STAS vs artifacts was available internationally for 6 days to Pulmonary Pathology Society members, thoracic pathology course attendees, and International Association for the Study of Lung Cancer pathology committee members. Additional 4 questions gathered demographic and practice setting information. One hundred thirty-six unique responses were analyzed. The majority were from North America and Europe (42.6% and 30.2%), practicing pulmonary pathology (70.6%) in academia (64.7%), and with >20 years of experience (31.6%). Excluding trainees, the greatest overall agreement was in defining solid and micropapillary tumor clusters of STAS located ≥3 alveolar spaces from the main tumor edge (91.5%) and recognizing strips of ciliated cells as artifacts (97.7%). Lesser agreement on STAS was evident when tumor cell clusters were immediately adjacent to the tumor edge, a single tumor cell cluster was present at the tissue edge, tumor cell clusters were jagged edged, or tumor cell clusters were admixed with ciliated cell strips (artifacts). There was no significant difference in agreements on STAS for multiple criteria between pulmonary and general pathologists. Significant interresponder agreement on STAS vs artifacts was achieved only for a few criteria. To improve the reproducibility of STAS vs artifacts, areas of lesser agreement require further clarification.