Interobserver agreement on what constitutes visceral pleural invasion by non-small cell lung carcinoma

Visceral pleural invasion (VPI) increases the T category of non-small cell lung carcinomas (NSCLCs) that otherwise only meet T1 criteria to T2. The American Joint Committee on Cancer provides no guidelines on what constitutes VPI. Penetration beyond the visceral pleural elastic layer (VPEL) has been proposed as the minimum criterion but is not internationally accepted. The purposes of this study were to elucidate current international practices regarding assessment of VPI and identify histologic features pathologists consider necessary for VPI. We examined responses to an online quiz consisting of 15 NSCLCs adjacent to or involving the visceral pleura. Of 103 participants from 22 countries, 84.5% were in academic practice; 42.7% had a subspecially interest in pulmonary pathology. Interobserver percentage agreement about whether VPI was present, absent, or indeterminate ranged from 36.9% to 93.2% (mean, 73.0%). The kappa for participants for all quiz cases was 0.35. There was considerable diagnostic variability in cases with extensive pleural elastosis and when tumor cells were intermingled with the VPEL. It seems that the majority of participants consider penetration of the VPEL necessary and also sufficient to categorize VPI as present. However, the formation of internationally recognized guidelines for assessing VPI by NSCLC is likely to improve diagnostic consensus.