[P-37] Intraobserver and interobserver agreement in the scoring of PD-L1 (SP142) and tumour-infiltrating lymphocytes in triple-negative breast cancers

David Jerome P. Ong, Pier Angeli dR Medina, Sarah Jane L. Datay-Lim and Elizabeth Ann S. Alcazaren

The Medical City, Ortigas Avenue, Pasig City, Philippines

Background and Objectives: Known for their poor outcomes, triple-negative breast cancers (TNBCs) have been investigated for immune checkpoint inhibitors that target Programmed death ligand 1 (PD-L1). In the recent decade, tumour-infiltrating lymphocytes (TILs) have also become potential biomarkers. The aim of the study was to determine the reproducibility of PD-L1 scoring system and TILs interpretation in the local setting through intra- and interobserver agreement.

Materials and Methods: Forty-three specimens were evaluated with PD-L1 (Roche VENTANA SP142 assay) and evaluated on two occasions by three pathologists. Kappa statistic for PD-L1 and TILs categories while intraclass correlation coefficient (ICC) were assessed, with cut-offs of 0.80 and 0.70, respectively.

Results: The overall kappa values for PD-L1 on the first and second rounds were weak at 0.506 (p = 0.000) and minimal at 0.315 (p = 0.002), respectively. Intraobserver kappa values for PD-L1 were varied across the three readers while interobserver kappa values for PD-L1 showed none (0.181) to moderate (0.789) agreement. The TILs intraobserver reliability showed poor to good agreement, with the highest ICC of 0.889 (95% CI: 0.805 - 0.938).

Conclusion: This study demonstrated variable intra- and interobserver agreement for both TILs and PD-L1 expression. Although it was desirable to have strong to almost perfect agreement, the kappa and ICC values suggested additional room for improvement. In light of the repercussions, the management of patients will undergo immune checkpoint inhibitor therapy, regular training sessions, concurrences of equivocal results and possible use of digital pathology as a medium in interpreting TILs and PD-L1 stains to achieve consistent results.