EP1.09-03 Interobserver Variability Study of PD-L1 Immunostaining in Non-Small Cell Lung Cancer

Abstract

Pathologic assessment of programmed cell death ligand 1 (PD-L1) immunohistochemical staining now have been used for treatment of non-small cerll lung cancer in advanced stage. But, due to misinterpretation or unspecified staining pattern, interpretation of PD-L1 staining may be difficult. This study was to investigate interobserver variability between three different pathologists to see if the staining can be safely assessed in practice. PD-L1 immunostaining (SP263 and SP142) was performed in representative sections of 70 adenocarcinoma cases and 58 squamous cell carcinoma cases which surgically resected at the chonnam National University Hwasun Hospital, Republic of Korea between 2013 to 2015. Three pathologists individually evaluated the percentage of positive tumor cells, scoring each sample applying cutoff levels used in clinical practice: <1% positive tumor cells (score 0), 1–4% (score 1), 5–9% (score 2), 10–49% (score 3), and >50% positive tumor cells (score 4). Three pathologists were in agreement in 121 of 128 (94.5%) of scored cases in the SP263 test and 109 of 128 (85.2%) in the SP142 test. In 26 remaining cases, at least two pathologists were in aggrement of scored cases. Weighted kappa value for interobserver variability between pathologists was respectively 0.892 in the SP263 test and 0.837 in the SP142 test. The number of differently classified cases was significantly higher for the ≥1% cutoff value than every other cutoff value. Also, a significantly better agreement between pathologists was seen using ≥50% as cutoff. No statistically significant differences were seen between adenocarcinoma and squamous cell carcinoma. Interobserver agreement remains an important challenge, and the ≥1% cutoff value seems to be problematic. But, this may be overcome by training, longer experience and optimization of cutoff value.