Clinical evaluation of a laboratory-developed test using clone E1L3N for the detection of PD-L1 expression status in non-small cell lung cancer

Background: Programmed death ligand 1 (PD-L1) has been used as a diagnostic marker to identify patients that will benefit from immune checkpoint inhibitors in non-small cell lung cancer (NSCLC). Immunohistochemistry with E1L3N clone is one of the most widely used and inexpensive laboratory-developed tests for PD-L1, but still need to be compared and validated with standard methods for clinical application. Methods: We investigated the performance of E1L3N clone for PD-L1 testing in 299 tumor tissues of NSCLC patients and its comparability with FDA-approved 22C3 clone. Results: The results show that the negative coincidence rate, weak positive coincidence rate, and positive coincidence rate were 97.4%, 92.2%, and 97.6% using the E1L3N assay relative to the 22C3 assay, respectively. An overall agreement of 96.3% was achieved between these two assays. We also found that the overall concordances were 97.8% and 93.9% for PD-L1 detection in large and small specimens, respectively, and no significant difference was obtained between these two assays (p = 0.076). In addition, the expression of PD-L1 was not detected in tumor tissues of benign lung disease using both the E1L3N and 22C3 assays. Conclusion: E1L3N can be used as a reliable alternative antibody clone to evaluate PD-L1 expression status for NSCLC patients.