PD-L1 expression in locally advanced cervical cancer: A pilot cross clone comparison study.

Purpose: Recent immunotherapy trials in locally advanced cervical cancer report high PD-L1 positivity rates whereas academic multicentric initiatives report a lower PD-L1 positivity. These observations necessitate cross-clone comparison to understand the observed differences.

Methods: Two different clones used in previous multicentric international studies SP142 (BIOEMBRACE) and 22C3 (KEYNOTE-A18) were used to test PD-L1 positivity in a pilot cohort of FIGO 2018 stage III cervical cancer patients recruited in a phase III trial. SP-142 IHC results were already available and negative and positive samples were included in 2:1 ratio. Biopsy material was processed for PD-L1 immunohistochemistry (IHC) using clone 22C3 pharmDx Combined Positivity Score (CPS≥ 1) with either antibody was considered positive. Positive and negative predictive value was calculated for each antibody while using the other as the reference.

Results: For the study, 20 PD-L1 negative and 10 PD-L1 positive (SP142) samples were included. The pilot positivity of the a priori selected cohort was 33.3%. PD-L1 positivity rate was 36.6% (11/30) using 22C3. Amongst the 20 SP142 negative patients, 6 patient samples (30%) tested positive on PD-L1 IHC with 22C3 leading to a 70% negative predictive rate for SP142. Five patient samples that were positive on SP142 did not test positive on 22C3 leading to positive predictive value of 50% while presuming 22C3 as the reference standard. The positive and negative predictive value of 22C3 (while taking SP142 as a reference) was 45% and 73% respectively.

Conclusion: Our findings highlight the differences in PD-L1 expression when different antibody clones are used for PD-L1 IHC. Though overall positivity rate was not different, there was heterogeneity at per patient level. Further investigation is needed into PD-L1 expression.