Reduced Tumour Proportion Scores for Programmed Cell Death Ligand 1 in Stored Paraffin Tissue Sections.

BACKGROUND/AIM: We evaluated the effects of storage of formalin-fixed, paraffin-embedded (FFPE) sections on the tumour proportion score (TPS) for programmed cell death ligand 1 (PD-L1), as indicator in non-small cell lung cancer (NSCLC) tissues of treatment efficacy.

MATERIALS AND METHODS: NSCLC postoperative specimens with PD-L1 TPS ≥50% were obtained and cut into five serial sections. One section was stained immediately, and four were stored at 4°C for 2, 4, 6, or 8 weeks. Slides were subjected to PD-L1 immunohistochemistry using the anti-PD-L1 clone 28-8. PD-L1 TPS were blindly evaluated by two independent pathologists.

RESULTS: Twelve specimens (60 slides) were evaluated. After slide storage for 2, 4, 6, and 8 weeks, a TPS of <50% was obtained in five (41%), four (33%), seven (58%), and eight (67%) patients, respectively.

CONCLUSION: TPS values for PD-L1 were reduced by long-term slide storage of FFPE specimens. Sectioned slides should be stained for PD-L1 without delay.