Profile of programmed death ligand-1 (PD-L1) expression and PD-L1 gene amplification in Indonesian colorectal cancer patients.

82Background: The presence of the programmed death ligand-1 (PD-L1) has been used as biomarker to select patients and analyze responses to anti-PD-1/L1 antibodies. PD-L1 positivity may be a result of genetic mechanism leading to constitutive PD-L1 expression or inducible mechanism by T-cell presence. Each mechanism may have different significance and response to such therapy. In colorectal cancer (CRC), targeting immune checkpoint inhibitor has been recommended for patients with microsatellite instable (MSI). This study aimed to investigate the mechanism of PD-L1 gene activation in colorectal cancer (CRC) patients, particularly in MSI population. Methods: We have investigated 61 archived formalin fixed paraffin embedded CRC specimens of patients from Medistra Hospital, Jakarta admitted in 2010 - 2016. Immunohistochemistry was performed to measure expression of PD-L1 in tumor cells as well as MSI status using antibodies against PD-L1 and MMR (MLH1, MSH2, PMS2 and MSH6), respectively. Subset of PD-L1 positi...